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Hamish
Guest
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 Posted: Sun Jan 02, 2005 5:34 am Post subject: Strange std::vector behaviour |
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Hello, lately I've been having a lot of trouble with the std::vector. Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Switch> Switches;
Now I have a for...loop:
int h = Switches.size();
for(int i=0;i
/*do stuff here*/
}
The problem is, when h (Switches.size()) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
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Cy Edmunds
Guest
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| Posted: Sun Jan 02, 2005 5:47 am Post subject: Re: Strange std::vector behaviour |
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"Hamish" <h.dean (AT) xtra (DOT) co.nz> wrote
| Quote: | Hello, lately I've been having a lot of trouble with the std::vector.
Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Switch> Switches;
Now I have a for...loop:
int h = Switches.size();
for(int i=0;i<Switches.size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size()) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
|
std::vector
something like 0xffffffff
--
Cy
http://home.rochester.rr.com/cyhome/
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Chris
Guest
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| Posted: Sun Jan 02, 2005 7:36 am Post subject: Re: Strange std::vector behaviour |
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"Cy Edmunds" <cedmunds (AT) spamless (DOT) rochester.rr.com> wrote
| Quote: | "Hamish" <h.dean (AT) xtra (DOT) co.nz> wrote in message
news:kJLBd.4441$mo2.257280 (AT) news (DOT) xtra.co.nz...
Hello, lately I've been having a lot of trouble with the std::vector.
Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Switch> Switches;
Now I have a for...loop:
int h = Switches.size();
for(int i=0;i<Switches.size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size()) equals 0, the for...loop is
still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
std::vector
something like 0xffffffff
|
or, you could use iterators:
typedef std::vector< Switch > tSwitchContainer
typedef tSwitchContainer::iterator tSwitchItr;
tSwitchContainer Switches;
for ( tSwitchItr cur = Switches.begin(); cur != Switches.end(); cur++)
{
// do stuff.....
}
nice thing about this is you could use any container and the code would
still work
-c
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Ioannis Vranos
Guest
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| Posted: Sun Jan 02, 2005 11:47 am Post subject: Re: Strange std::vector behaviour |
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Hamish wrote:
| Quote: | Hello, lately I've been having a lot of trouble with the std::vector. Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Switch> Switches;
Now I have a for...loop:
int h = Switches.size();
for(int i=0;i<Switches.size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size()) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
|
Switches.size() returns a vector
integer type.
Thus vector<Switch>::size_type(-1) is the maximum value of that type.
Your code can be fixed like this:
for(int i=0; i<Switches.size(); ++i)
/*do stuff here*/
or better:
for(vector
/*do stuff here*/
--
Ioannis Vranos
http://www23.brinkster.com/noicys
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Mike Wahler
Guest
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| Posted: Sun Jan 02, 2005 11:30 pm Post subject: Re: Strange std::vector behaviour |
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"Hamish" <h.dean (AT) xtra (DOT) co.nz> wrote
| Quote: | Hello, lately I've been having a lot of trouble with the std::vector.
Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Switch> Switches;
Now I have a for...loop:
int h = Switches.size();
for(int i=0;i<Switches.size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size()) equals 0, the for...loop is still
entered, and runs infinitely.
|
for(std::vector
/* etc */
If for some reason you really want to ignore the last
element (if one exists):
if(!Switches.empty())
for(std::vector
/* etc */
| Quote: |
However, if I use the line:
for(int i=0;i
then there is not a problem.
|
If 'h' starts at zero, the behavior is undefined.
| Quote: |
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
|
Vector indices begin with zero and run through 'size()' - 1
-Mike
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Ioannis Vranos
Guest
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| Posted: Mon Jan 03, 2005 12:55 am Post subject: Re: Strange std::vector behaviour |
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Hamish wrote:
| Quote: | Hello, lately I've been having a lot of trouble with the std::vector. Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Switch> Switches;
Now I have a for...loop:
int h = Switches.size();
for(int i=0;i<Switches.size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size()) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
|
Switches.size() returns a vector
integer type.
Thus vector<Switch>::size_type(-1) is the maximum value of that type.
Your code can be fixed like this:
for(int i=0; i<Switches.size(); ++i)
/*do stuff here*/
or better:
for(vector
/*do stuff here*/
--
Ioannis Vranos
http://www23.brinkster.com/noicys
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E. Mark Ping
Guest
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| Posted: Fri Mar 25, 2005 6:24 am Post subject: Re: Strange std::vector behaviour |
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In article <Su%Bd.15657$RH4.3076 (AT) newsread1 (DOT) news.pas.earthlink.net>,
Mike Wahler <mkwahler (AT) mkwahler (DOT) net> wrote:
| Quote: | If for some reason you really want to ignore the last
element (if one exists):
if(!Switches.empty())
for(std::vector<Switch>::size_type i = 0; i < Switches.size() - 1; ++i)
/* etc */
|
Which of course is a big problem if the size is 0. When dealing with
unsigned types, I find avoiding subtraction to be much safer.
for(int i = 0; i+1 < Switches.size(); ++i)
--
Mark Ping
[email]emarkp (AT) soda (DOT) CSUA.Berkeley.EDU[/email]
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John Carson
Guest
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| Posted: Fri Mar 25, 2005 8:22 am Post subject: Re: Strange std::vector behaviour |
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"E. Mark Ping" <emarkp (AT) soda (DOT) csua.berkeley.edu> wrote
| Quote: | In article <Su%Bd.15657$RH4.3076 (AT) newsread1 (DOT) news.pas.earthlink.net>,
Mike Wahler <mkwahler (AT) mkwahler (DOT) net> wrote:
If for some reason you really want to ignore the last
element (if one exists):
if(!Switches.empty())
for(std::vector<Switch>::size_type i = 0; i < Switches.size() - 1;
++i) /* etc */
Which of course is a big problem if the size is 0.
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You seem not to have noticed the test:
if(!Switches.empty())
--
John Carson
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