C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  vector functions          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Michael Sgier Guest Posted: Tue Sep 27, 2005 4:11 pm    Post subject: vector functions Hello If someone could explain the code below to me would be great. // return angle between two vectors const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } This is producing the following errors: vector.h:220: error: declaration does not declare anything vector.h:220: error: syntax error before `inline' vector.h:226: error: ISO C++ forbids defining types within return type vector.h:226: error: syntax error before `inline' vector.h:233: error: syntax error before `inline' vector.h:236: error: `angle' was not declared in this scope vector.h:238: error: syntax error before `return' What do % and ^ produce? Why is there a const also at the end of the function definition? THANKS and regards Michael Back to top Christian Meier Guest Posted: Tue Sep 27, 2005 4:18 pm    Post subject: Re: vector functions "Michael Sgier" <sgier (AT) nospam (DOT) ch> schrieb im Newsbeitrag news:43396eaa$0$1150$5402220f (AT) news (DOT) sunrise.ch... Quote: Hello If someone could explain the code below to me would be great. // return angle between two vectors const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } This is producing the following errors: vector.h:220: error: declaration does not declare anything vector.h:220: error: syntax error before `inline' vector.h:226: error: ISO C++ forbids defining types within return type vector.h:226: error: syntax error before `inline' vector.h:233: error: syntax error before `inline' vector.h:236: error: `angle' was not declared in this scope vector.h:238: error: syntax error before `return' Paste your whole class. Or better: Reduce your code as much as possible and then paste your class here. Quote: What do % and ^ produce? % is the modulus operator. It returns the remainder of a division. ^ is the bitwise-exclusive-or operator. It compares each bit. If one of them is 0 and the other one is 1, the corresponding bit in the result is also 1, otherwise it is 0. Quote: Why is there a const also at the end of the function definition? Functions of a class are not allowed to modify the member variables if a function was declared as const. Quote: THANKS and regards Michael Greetings Chris Back to top Kai-Uwe Bux Guest Posted: Tue Sep 27, 2005 5:16 pm    Post subject: Re: vector functions Christian Meier wrote: Quote: "Michael Sgier" <sgier (AT) nospam (DOT) ch> schrieb im Newsbeitrag news:43396eaa$0$1150$5402220f (AT) news (DOT) sunrise.ch... Hello If someone could explain the code below to me would be great. // return angle between two vectors const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } This is producing the following errors: vector.h:220: error: declaration does not declare anything vector.h:220: error: syntax error before `inline' vector.h:226: error: ISO C++ forbids defining types within return type vector.h:226: error: syntax error before `inline' vector.h:233: error: syntax error before `inline' vector.h:236: error: `angle' was not declared in this scope vector.h:238: error: syntax error before `return' Paste your whole class. Or better: Reduce your code as much as possible and then paste your class here. What do % and ^ produce? % is the modulus operator. It returns the remainder of a division. ^ is the bitwise-exclusive-or operator. It compares each bit. If one of them is 0 and the other one is 1, the corresponding bit in the result is also 1, otherwise it is 0. Well, I am inclined to bet that these operators are overloaded in that vector class to compute the scalar product and the cross product, and I also suspect that operator! has been tweaked to compute the norm of the vector and that operator| rescales a vector to a given length. Best Kai-Uwe Bux Back to top persenaama Guest Posted: Tue Sep 27, 2005 5:22 pm    Post subject: Re: vector functions /* const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } */ Above the % should be scalar product so that the angle between *this and normal would be computed, it's generally a bad to use % for cross product, which it is often seen used in code like this. Using it for dot/scalar product is even more strange. Just commenting on that oddity, I could comment on the errors if I knew which line was which (eg. which error correspond to which line). I bet somewhere along the line some declaration was missed (maybe the headers are not self-contained or require specific order of inclusion, whatever, beats me w/o seeing more of the code.. :) Back to top persenaama Guest Posted: Tue Sep 27, 2005 5:25 pm    Post subject: Re: vector functions I just cannot resisting replying again.. I keep staring at the code in disbelief: really bizarre use of operator overloading. +, -, /, * .. are are still cool and useful since the meaning is easily understood, but... what is happening here is beyond belief.. incredible stuff.. no offence! 8P Back to top Richard Herring Guest Posted: Tue Sep 27, 2005 5:26 pm    Post subject: Re: vector functions In message <dhbrdr$17m$1 (AT) news (DOT) hispeed.ch>, Christian Meier <chris (AT) gmx (DOT) ch> writes Quote: "Michael Sgier" <sgier (AT) nospam (DOT) ch> schrieb im Newsbeitrag news:43396eaa$0$1150$5402220f (AT) news (DOT) sunrise.ch... Hello If someone could explain the code below to me would be great. // return angle between two vectors const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } This appears to be a member function. So what's the declaration of the class of which it's a member? We're not mind-readers here. Quote: // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } This is producing the following errors: vector.h:220: error: declaration does not declare anything So which of the above is line 220? We're not mind-readers here. Quote: vector.h:220: error: syntax error before `inline' vector.h:226: error: ISO C++ forbids defining types within return type vector.h:226: error: syntax error before `inline' vector.h:233: error: syntax error before `inline' vector.h:236: error: `angle' was not declared in this scope vector.h:238: error: syntax error before `return' Paste your whole class. Or better: Reduce your code as much as possible and then paste your class here. What do % and ^ produce? % is the modulus operator. It returns the remainder of a division. ^ is the bitwise-exclusive-or operator. It compares each bit. If one of them is 0 and the other one is 1, the corresponding bit in the result is also 1, otherwise it is 0. Not quite. % and ^ applied to built-in types do as you say. Here the operands are of type CVector, whatever that is. My guess is that the author of the class CVector has overloaded those operators (and also operator| and operator*) to make them perform some completely unrelated function. Which is, of course, *EVIL*. Quote: Why is there a const also at the end of the function definition? Functions of a class are not allowed to modify the member variables if a function was declared as const. -- Richard Herring Back to top Kai-Uwe Bux Guest Posted: Wed Sep 28, 2005 12:39 am    Post subject: Re: vector functions Richard Herring wrote: Quote: In message <dhbrdr$17m$1 (AT) news (DOT) hispeed.ch>, Christian Meier [email]chris (AT) gmx (DOT) ch[/email]> writes "Michael Sgier" <sgier (AT) nospam (DOT) ch> schrieb im Newsbeitrag news:43396eaa$0$1150$5402220f (AT) news (DOT) sunrise.ch... [snip] // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } [snip] % is the modulus operator. It returns the remainder of a division. ^ is the bitwise-exclusive-or operator. It compares each bit. If one of them is 0 and the other one is 1, the corresponding bit in the result is also 1, otherwise it is 0. Not quite. % and ^ applied to built-in types do as you say. Here the operands are of type CVector, whatever that is. My guess is that the author of the class CVector has overloaded those operators (and also operator| and operator*) to make them perform some completely unrelated function. Which is, of course, *EVIL*. I beg to differ. It is not evil; it is the legitimate attempt to make the math in your code resemble the math from your text book as closely as possible. This, makes it indeed easier to maintain the code (after some learning curve). The fact that one can actually guess what the operators in the OPs code are doing supports this hypothesis: CVector operator| ( double length ) const; // rescale a vector to length double operator% ( CVector const & other ) const; // scalar product double operator! ( void ) const; // norm CVector operator^ ( CVector const & other ) const; // cross product [operator* appears to denote a projection, and I have to admit that the use of an operator for this is questionable as you usually will not find infix notation for projections in math texts.] Whether operator overloading is moral or evil is a cultural question, and the correct answer is very much context dependent. Operator overloading in C++ allows you to implement special purpose sublanguages. Admittedly, this is a double edged sword. In the context of math programming, I find it by and large very helpful. Best Kai-Uwe Bux Back to top Christian Meier Guest Posted: Wed Sep 28, 2005 6:05 am    Post subject: Re: vector functions "Kai-Uwe Bux" <jkherciueh (AT) gmx (DOT) net> schrieb im Newsbeitrag news:dhbupe$mmi$1 (AT) murdoch (DOT) acc.Virginia.EDU... Quote: Christian Meier wrote: "Michael Sgier" <sgier (AT) nospam (DOT) ch> schrieb im Newsbeitrag news:43396eaa$0$1150$5402220f (AT) news (DOT) sunrise.ch... Hello If someone could explain the code below to me would be great. // return angle between two vectors const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } This is producing the following errors: vector.h:220: error: declaration does not declare anything vector.h:220: error: syntax error before `inline' vector.h:226: error: ISO C++ forbids defining types within return type vector.h:226: error: syntax error before `inline' vector.h:233: error: syntax error before `inline' vector.h:236: error: `angle' was not declared in this scope vector.h:238: error: syntax error before `return' Paste your whole class. Or better: Reduce your code as much as possible and then paste your class here. What do % and ^ produce? % is the modulus operator. It returns the remainder of a division. ^ is the bitwise-exclusive-or operator. It compares each bit. If one of them is 0 and the other one is 1, the corresponding bit in the result is also 1, otherwise it is 0. Well, I am inclined to bet that these operators are overloaded in that vector class to compute the scalar product and the cross product, and I also suspect that operator! has been tweaked to compute the norm of the vector and that operator| rescales a vector to a given length. Of course they are overloaded. Well not "of course", but I am quite sure, too. Fact is, we do not have any code. Another fact is, that the source above does not compile. So, without more code and without guesses the operators want to do, what I described. If he wants to know what does operator do with *this, he has to paste more code of the class, as I mentioned. OK, where do we know if this code is inside a class? The keyword inline is a bit confusing. It would not be necessary if this were a class.... Anyway, to be sure, we need more code. Quote: Best Kai-Uwe Bux Greetings Chris Back to top Michael Sgier Guest Posted: Wed Sep 28, 2005 7:34 am    Post subject: Re: vector functions Hello again here's more code with the copyright. I've cutted out the parts that i've believed to have understood. I would be very grateful for any explanations on the following especially where i marked my questions. ( and of course the resolving of the errors. The error messages were put to the corresponding line where they appeared to the end of the code. ) THANKS and regards Michael #ifndef __VECTOR_H #define __VECTOR_H #include <math.h> /* VECTOR.H CVector class Some operators of the CVector class based on operators of the CVector class by Bas Kuenen. Copyright (c) 2000 Bas Kuenen. All Rights Reserved. homepage: baskuenen.cfxweb.net */ #define PI (3.14159265359f) #define DEG2RAD(a) (PI/180*(a)) #define RAD2DEG(a) (180/PI*(a)) typedef float scalar_t; class CVector { public: scalar_t x; scalar_t y; scalar_t z; // x,y,z coordinates public: CVector(scalar_t a = 0, scalar_t b = 0, scalar_t c = 0) : x(a), y(b), z(c) {} // what does the : here? CVector(const CVector &vec) : x(vec.x), y(vec.y), z(vec.z) {} // vector index scalar_t &operator[](const long idx) { return *((&x)+idx); } // vector assignment const CVector &operator=(const CVector &vec) // I don't really understand: (const CVector &vec) ??? { x = vec.x; y = vec.y; z = vec.z; return *this; } // vector add const CVector operator+(const CVector &vec) const { return CVector(x + vec.x, y + vec.y, z + vec.z); } // vector add (opposite of negation) const CVector operator+() const // hmmmm???? same to the following ones { return CVector(*this); } // scalar self-divecide const CVector &operator/=(const scalar_t &s) { const float recip = 1/s; // for speed, one divecision x *= recip; y *= recip; z *= recip; return *this; } // pre multiply by scalar friend inline const CVector operator*(const scalar_t &s, const CVector &vec) { return vec*s; } const CVector operator*(const CVector& vec) const { return CVector(x*vec.x, y*vec.y, z*vec.z); } // post multiply by scalar /*friend inline const CVector operator*(const CVector &vec, const scalar_t &s) { return CVector(vec.x*s, vec.y*s, vec.z*s); }*/ // divide by scalar const CVector operator/(scalar_t s) const { s = 1/s; return CVector(s*x, s*y, s*z); } // dot product const scalar_t DotProduct(const CVector &vec) const { return x*vec.x + y*vec.x + z*vec.z; } // dot product const scalar_t operator%(const CVector &vec) const // why two functions? { return x*vec.x + y*vec.x + z*vec.z; } // normalize this vector void Normalize() { (*this) /= Length(); //humm??? } const scalar_t operator!() const // why "const CVector &vec" was omitted? { return sqrtf(x*x + y*y + z*z); } // return vector with specified length const CVector operator | (const scalar_t length) const { return *this * (length / !(*this)); } // set length of vector equal to length const CVector& operator |= (const float length) { return *this = *this | length; // what's the Quote: here? } // return angle between two vectors //those errors here at next line //vector.h:220: error: declaration does not declare anything //vector.h:220: error: syntax error before `inline' const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } // reflect this vector off surface with normal vector //those errors here at next line //vector.h:226: error: ISO C++ forbids defining types within return type //vector.h:226: error: syntax error before `inline' const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal //those errors here at next line //vector.h:233: error: syntax error before `inline' const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); //those errors here at next line //vector.h:236: error: `angle' was not declared in this scope const float sine = sinf(angle); //those errors here at next line //vector.h:238: error: syntax error before `return' return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } }; #endif Back to top John Harrison Guest Posted: Wed Sep 28, 2005 7:53 am    Post subject: Re: vector functions Michael Sgier wrote: Quote: Hello again here's more code with the copyright. I've cutted out the parts that i've believed to have understood. I would be very grateful for any explanations on the following especially where i marked my questions. ( and of course the resolving of the errors. The error messages were put to the corresponding line where they appeared to the end of the code. ) Comments follow Quote: THANKS and regards Michael #ifndef __VECTOR_H #define __VECTOR_H #include /* VECTOR.H CVector class Some operators of the CVector class based on operators of the CVector class by Bas Kuenen. Copyright (c) 2000 Bas Kuenen. All Rights Reserved. homepage: baskuenen.cfxweb.net */ #define PI (3.14159265359f) #define DEG2RAD(a) (PI/180*(a)) #define RAD2DEG(a) (180/PI*(a)) typedef float scalar_t; class CVector { public: scalar_t x; scalar_t y; scalar_t z; // x,y,z coordinates public: CVector(scalar_t a = 0, scalar_t b = 0, scalar_t c = 0) : x(a), y(b), z(c) {} // what does the : here? CVector(const CVector &vec) : x(vec.x), y(vec.y), z(vec.z) {} // vector index scalar_t &operator[](const long idx) { return *((&x)+idx); } // vector assignment const CVector &operator=(const CVector &vec) // I don't really understand: (const CVector &vec) ??? This is standard. It says that the assignment operator for CVectors takes one argument by reference (& means by reference), and does not use that reference to alter the argument (that's what const means). This is what you would want from an assignment operator. Also notice that the copy constructor above is similar for similar reasons. Quote: { x = vec.x; y = vec.y; z = vec.z; return *this; } // vector add const CVector operator+(const CVector &vec) const { return CVector(x + vec.x, y + vec.y, z + vec.z); } // vector add (opposite of negation) const CVector operator+() const // hmmmm???? same to the following ones What's to hmmm? Again we have a const member function returning a const object. The member function is const because it does not alter the object. The return is const because if it were not then this code CVector v1, v2; +v1 = v2; would be legal. It's not a big issue because you would probably never write code like that, but I'm sure you agree there no harm in disallowing code like that. Quote: { return CVector(*this); } // scalar self-divecide const CVector &operator/=(const scalar_t &s) { const float recip = 1/s; // for speed, one divecision x *= recip; y *= recip; z *= recip; return *this; } // pre multiply by scalar friend inline const CVector operator*(const scalar_t &s, const CVector &vec) { return vec*s; } const CVector operator*(const CVector& vec) const { return CVector(x*vec.x, y*vec.y, z*vec.z); } // post multiply by scalar /*friend inline const CVector operator*(const CVector &vec, const scalar_t &s) { return CVector(vec.x*s, vec.y*s, vec.z*s); }*/ // divide by scalar const CVector operator/(scalar_t s) const { s = 1/s; return CVector(s*x, s*y, s*z); } // dot product const scalar_t DotProduct(const CVector &vec) const { return x*vec.x + y*vec.x + z*vec.z; } // dot product const scalar_t operator%(const CVector &vec) const // why two functions? { return x*vec.x + y*vec.x + z*vec.z; } Good question. Drop the operator% would be my advice. Quote: // normalize this vector void Normalize() { (*this) /= Length(); //humm??? } Seems reasonable to me, divide a vector by it's length, resulting is a vector of length 1. What's the problem? Quote: const scalar_t operator!() const // why "const CVector &vec" was omitted? { return sqrtf(x*x + y*y + z*z); } Because operator! operates on a single CVector, not two CVector's. Quote: // return vector with specified length const CVector operator | (const scalar_t length) const { return *this * (length / !(*this)); } // set length of vector equal to length const CVector& operator |= (const float length) { return *this = *this | length; // what's the | here? } It calls the function declared immediately above this one. The one with the comment 'return vector with specified length'. In general if you define operator@ you should also define operator @=, this is what is being done here. operator| is defined then operator|= is defined so that is calls operator|. Quote: // return angle between two vectors //those errors here at next line //vector.h:220: error: declaration does not declare anything //vector.h:220: error: syntax error before `inline' const float inline Angle(const CVector& normal) const { return acosf(*this % normal); } inline is illegal here, remove it. Should be fine then. Quote: // reflect this vector off surface with normal vector //those errors here at next line //vector.h:226: error: ISO C++ forbids defining types within return type //vector.h:226: error: syntax error before `inline' const CVector inline Reflection(const CVector& normal) const Ditto. Quote: { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal //those errors here at next line //vector.h:233: error: syntax error before `inline' const CVector inline Rotate(const float angle, const CVector& normal) const Ditto. Quote: { const float cosine = cosf(angle); //those errors here at next line //vector.h:236: error: `angle' was not declared in this scope const float sine = sinf(angle); //those errors here at next line //vector.h:238: error: syntax error before `return' return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } }; #endif john Back to top John Harrison Guest Posted: Wed Sep 28, 2005 7:59 am    Post subject: Re: vector functions John Harrison wrote: Quote: Michael Sgier wrote: Hello again here's more code with the copyright. I've cutted out the parts that i've believed to have understood. I would be very grateful for any explanations on the following especially where i marked my questions. It's pretty clear that operator overloading is a bit of a mystery to you. But there is no mystery, overloaded operators are just function calls with a different syntax. That is pretty much all there is to it. CVector a , b, c; a + b; // call overloaded + operator (two parameters) !a; // call overloaded ! operator (one parameter) a = b; // call overloaded = operator (two parameters) c = a % b; // call overloaded % operator, which returns a result, which is then used as a parameter to the overloaded = operator. In the above +, !, = and % are just functions (or member functions). john Back to top Christian Meier Guest Posted: Wed Sep 28, 2005 8:12 am    Post subject: Re: vector functions "John Harrison" <john_andronicus (AT) hotmail (DOT) com> schrieb im Newsbeitrag news:f_r_e.27$0f3.9 (AT) newsfe1-win (DOT) ntli.net... Quote: Michael Sgier wrote: Hello again here's more code with the copyright. I've cutted out the parts that i've believed to have understood. I would be very grateful for any explanations on the following especially where i marked my questions. ( and of course the resolving of the errors. The error messages were put to the corresponding line where they appeared to the end of the code. ) Comments follow THANKS and regards Michael #ifndef __VECTOR_H #define __VECTOR_H #include /* VECTOR.H CVector class Some operators of the CVector class based on operators of the CVector class by Bas Kuenen. Copyright (c) 2000 Bas Kuenen. All Rights Reserved. homepage: baskuenen.cfxweb.net */ #define PI (3.14159265359f) #define DEG2RAD(a) (PI/180*(a)) #define RAD2DEG(a) (180/PI*(a)) typedef float scalar_t; class CVector { public: scalar_t x; scalar_t y; scalar_t z; // x,y,z coordinates public: CVector(scalar_t a = 0, scalar_t b = 0, scalar_t c = 0) : x(a), y(b), z(c) {} // what does the : here? CVector(const CVector &vec) : x(vec.x), y(vec.y), z(vec.z) {} Seems that you did not see this question. In constructors you have an initializer part. After CVector() : x(0) {} you have the same as after CVector() { x = 0; } In your constructor CVector(scalar_t a = 0, scalar_t b = 0, scalar_t c = 0) you have three default arguments. So, if you instantiate CVector without arguments, then your x, y and z are 0. The rest was answered. Greetings Chris Back to top Karl Heinz Buchegger Guest Posted: Wed Sep 28, 2005 9:03 am    Post subject: Re: vector functions John Harrison wrote: Quote: John Harrison wrote: Michael Sgier wrote: Hello again here's more code with the copyright. I've cutted out the parts that i've believed to have understood. I would be very grateful for any explanations on the following especially where i marked my questions. It's pretty clear that operator overloading is a bit of a mystery to you. But there is no mystery, overloaded operators are just function calls with a different syntax. That is pretty much all there is to it. CVector a , b, c; a + b; // call overloaded + operator (two parameters) !a; // call overloaded ! operator (one parameter) a = b; // call overloaded = operator (two parameters) c = a % b; // call overloaded % operator, which returns a result, which is then used as a parameter to the overloaded = operator. In the above +, !, = and % are just functions (or member functions). To the OP: It becomes clearer this way: a + b is equivalent to (if the operator is a member function of the class) a.operator+( b ) Here one can see the function call explicitely. If the operator is a freestanding function, then the above becomes: operator+( a, b ); Another example: c = a + b; with all operators as member functions: c.operator=( a.operator+( b ) ); or a free standing operator+ c.operator=( operator+( a, b ) ); Don't let yourself fool you with that special word 'operator'. They are just ordinary functions which can be used in a special 'call syntax' ( a + b instead of a.foo( b ) ). -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Richard Herring Guest Posted: Wed Sep 28, 2005 10:04 am    Post subject: Re: vector functions In message <dhcoo7$4s0$1 (AT) murdoch (DOT) acc.Virginia.EDU>, Kai-Uwe Bux <jkherciueh (AT) gmx (DOT) net> writes Quote: Richard Herring wrote: In message <dhbrdr$17m$1 (AT) news (DOT) hispeed.ch>, Christian Meier [email]chris (AT) gmx (DOT) ch[/email]> writes "Michael Sgier" <sgier (AT) nospam (DOT) ch> schrieb im Newsbeitrag news:43396eaa$0$1150$5402220f (AT) news (DOT) sunrise.ch... [snip] // reflect this vector off surface with normal vector const CVector inline Reflection(const CVector& normal) const { const CVector vec(*this | 1); // normalize this vector return (vec - normal * 2.0 * (vec % normal)) * !*this; } // rotate angle degrees about a normal const CVector inline Rotate(const float angle, const CVector& normal) const { const float cosine = cosf(angle); const float sine = sinf(angle); return CVector(*this * cosine + ((normal * *this) * (1.0f - cosine)) * normal + (*this ^ normal) * sine); } [snip] % is the modulus operator. It returns the remainder of a division. ^ is the bitwise-exclusive-or operator. It compares each bit. If one of them is 0 and the other one is 1, the corresponding bit in the result is also 1, otherwise it is 0. Not quite. % and ^ applied to built-in types do as you say. Here the operands are of type CVector, whatever that is. My guess is that the author of the class CVector has overloaded those operators (and also operator| and operator*) to make them perform some completely unrelated function. Which is, of course, *EVIL*. I beg to differ. It is not evil; it is the legitimate attempt to make the math in your code resemble the math from your text book as closely as possible. As closely as possible, certainly. But not more so :-( Quote: This, makes it indeed easier to maintain the code (after some learning curve). The fact that one can actually guess what the operators in the OPs code are doing supports this hypothesis: CVector operator| ( double length ) const; // rescale a vector to length I've never seen a special mathematical notation for that. The only clue is in the argument name, which is only visible in the declaration of the function, not its use. IMO a suitably-named function would be clearer. (Moreover I suspect that the right-hand operand will almost always be 1, in which case why not use operator~ to suggest the "hat" notation for taking a unit vector?) Quote: double operator% ( CVector const & other ) const; // scalar product Granted, operator. can't be overloaded, so some other symbol is needed, but there's nothing transparent about using something suggesting "remainder" for multiplication, especially as operator* would be the obvious choice. Quote: double operator! ( void ) const; // norm Hmm. If that's meant to suggest the |a| notation it's ambiguous: norm or abs? Personally I'd take a hint from the implementation of std::complex and go for a function called norm. Quote: CVector operator^ ( CVector const & other ) const; // cross product Fair enough. That, like + and -, matches the mathematical notation. Quote: [operator* appears to denote a projection, and I have to admit that the use of an operator for this is questionable as you usually will not find infix notation for projections in math texts.] Quite. The natural interpretation of * is a product, and as ^ naturally suggests cross product, I'd expect this to give the "other" product, i.e. the scalar one. Quote: Whether operator overloading is moral or evil is a cultural question, and the correct answer is very much context dependent. Operator overloading in C++ allows you to implement special purpose sublanguages. Admittedly, this is a double edged sword. In the context of math programming, I find it by and large very helpful. I think we must agree to differ. By all means overload operators if the operation is broadly the same as their conventional meaning, but if you're torturing the syntax by overloading an operator only because it isn't otherwise used and happens to have the right syntax, it's time to start thinking of sensibly-named functions. -- Richard Herring Back to top John Harrison Guest Posted: Wed Sep 28, 2005 5:08 pm    Post subject: Re: vector functions Quote: Seems that you did not see this question. Right I didn't. Seems to me that the OP is trying to write a substantial C++ program (or at least modify one) and hoping to learn C++ as they go along. I wouldn't wnat to discourage that (each to their own etc.) but a little simultaneous background reading wouldn't go amiss. 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