C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Converting string to integer          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Gil Guest Posted: Wed Jan 28, 2004 7:56 am    Post subject: Converting string to integer I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? Back to top Patrik Stellmann Guest Posted: Wed Jan 28, 2004 8:08 am    Post subject: Re: Converting string to integer Quote: I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? assuming you include stdlib.h and the string-class provides the cast-operator to const char*: int val = atoi(string); Back to top Sharad Kala Guest Posted: Wed Jan 28, 2004 8:25 am    Post subject: Re: Converting string to integer "Gil" <brightoceanlight (AT) hotmail (DOT) com> wrote Quote: I have a string : string A = "2"; I need to get it's integer value : Check http://www.groups.google.com Anyways, int main() { string str = "123"; istringstream iss(str); int x; iss >> x; if(iss) { // conversion successful } else { // could not convert str to an int } } Best wishes, Sharad Back to top Chris Theis Guest Posted: Wed Jan 28, 2004 8:32 am    Post subject: Re: Converting string to integer "Patrik Stellmann" <stellmann (AT) tu-harburg (DOT) de> wrote Quote: I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? assuming you include stdlib.h and the string-class provides the cast-operator to const char*: Sorry, but both of these assumptions are incorrect. The standard header to include is <cstdlib> nowadays. Furthermore the string class does not provide an implicit const char* conversion but rather the c_str() member function. Quote: int val = atoi(string); int val = atoi( A.c_str() ); should do the trick. Regards Chris Back to top Peter Koch Larsen Guest Posted: Wed Jan 28, 2004 9:14 am    Post subject: Re: Converting string to integer "Gil" <brightoceanlight (AT) hotmail (DOT) com> skrev i en meddelelse news:adc2ca29.0401272356.ed42b94 (AT) posting (DOT) google.com... Quote: I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? Do yourself two favours: 1) Get the FAQ for this newsgroup and read it all... it is well worth the effort. The faq can be found at http://www.parashift.com/c++-faq-lite/. 2) Get the boost-library (http://www.boost.org) and look at all the wonderful things it has to offer - among them the solution to your problem. Kind regards Peter Back to top Armando Guest Posted: Wed Jan 28, 2004 10:25 am    Post subject: Re: Converting string to integer [email]brightoceanlight (AT) hotmail (DOT) com[/email] (Gil) wrote in message news:<adc2ca29.0401272356.ed42b94 (AT) posting (DOT) google.com>... Quote: I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? hallo i think you can do so which the function atoi. int val = atoi(A); Armando Back to top Old Wolf Guest Posted: Wed Jan 28, 2004 8:19 pm    Post subject: Re: Converting string to integer Quote: I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? assuming you include stdlib.h and the string-class provides the cast-operator to const char*: Sorry, but both of these assumptions are incorrect. The standard header to include is <cstdlib> nowadays. Furthermore the string class does not provide an implicit const char* conversion but rather the c_str() member function. He didn't mention any details about his string class. Maybe you are confusing it with std::string ? Quote: int val = atoi( A.c_str() ); int val = std::atoi( A.c_str() ); nowadays. Back to top Jack Klein Guest Posted: Thu Jan 29, 2004 3:06 am    Post subject: Re: Converting string to integer On Wed, 28 Jan 2004 09:32:08 +0100, "Chris Theis" <Christian.Theis (AT) nospam (DOT) cern.ch> wrote in comp.lang.c++: Quote: "Patrik Stellmann" <stellmann (AT) tu-harburg (DOT) de> wrote in message news:bv7ql5$pch6m$1 (AT) uni-berlin (DOT) de... I have a string : string A = "2"; I need to get it's integer value : // ?? int val = A ; // ?? assuming you include stdlib.h and the string-class provides the cast-operator to const char*: Sorry, but both of these assumptions are incorrect. The standard header to include is <cstdlib> nowadays. Furthermore the string class does not provide an implicit const char* conversion but rather the c_str() member function. int val = atoi(string); int val = atoi( A.c_str() ); should do the trick. No, not really. The ato... functions from the C library should never be used unless you have already checked the character array and know that it will not result in a numeric value outside the range of the given type, in which case you might as well do the conversion yourself while you are walking the string. All of the ato... functions generate undefined behavior if the text string represents a numerical value outside the range of the type. That is exactly why the strto... functions were added during C standardization. They have defined behavior for all inputs, other than being passed a null pointer. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html Back to top Chris Theis Guest Posted: Thu Jan 29, 2004 7:58 am    Post subject: Re: Converting string to integer "Jack Klein" <jackklein (AT) spamcop (DOT) net> wrote Quote: On Wed, 28 Jan 2004 09:32:08 +0100, "Chris Theis" [email]Christian.Theis (AT) nospam (DOT) cern.ch[/email]> wrote in comp.lang.c++: [SNIP] No, not really. The ato... functions from the C library should never be used unless you have already checked the character array and know that it will not result in a numeric value outside the range of the given type, in which case you might as well do the conversion yourself while you are walking the string. All of the ato... functions generate undefined behavior if the text string represents a numerical value outside the range of the type. That is exactly why the strto... functions were added during C standardization. They have defined behavior for all inputs, other than being passed a null pointer. I didn't know that ato... might result in undefined behavior. Thanks for telling me, Jack. However, in C++ I would recommend to use stringstreams anyway. Cheers Chris Back to top Chris Theis Guest Posted: Thu Jan 29, 2004 8:01 am    Post subject: Re: Converting string to integer "Old Wolf" <oldwolf (AT) inspire (DOT) net.nz> wrote Quote: I have a string : string A = "2"; [SNIP] He didn't mention any details about his string class. Maybe you are confusing it with std::string ? The OP declared his string using a class named "string". Without any further specification it is valid (at least IMHO) to presume that the standard string class is meant. Anyway, naming your own string class like the standard one is certainly not the cleverest idea, don't you think? Quote: int val = std::atoi( A.c_str() ); nowadays. Only if no using namespace statement has been issued, which cannot be verified from the code snippet. Chris Back to top Default User Guest Posted: Thu Jan 29, 2004 5:07 pm    Post subject: Re: Converting string to integer Chris Theis wrote: Quote: The OP declared his string using a class named "string". Without any further specification it is valid (at least IMHO) to presume that the standard string class is meant. Anyway, naming your own string class like the standard one is certainly not the cleverest idea, don't you think? I don't even think it's a legal identifier. I believe that in C++, like C, all identifiers beginning with "str" and followed by a letter are reserved. Brian Rodenborn Back to top red floyd Guest Posted: Thu Jan 29, 2004 8:35 pm    Post subject: Re: Converting string to integer Default User wrote: Quote: Chris Theis wrote: [redacted] I don't even think it's a legal identifier. I believe that in C++, like C, all identifiers beginning with "str" and followed by a letter are reserved. Say what??????????????? Can you quote chapter and verse from the Holy Standard (or the Holy C standard) on that one? That would break any code that uses "strange", "strong", "stretch", etc.. as variables. Back to top Ron Natalie Guest Posted: Thu Jan 29, 2004 9:03 pm    Post subject: Re: Converting string to integer "red floyd" <no.spam (AT) here (DOT) dude> wrote Quote: Default User wrote: Chris Theis wrote: [redacted] I don't even think it's a legal identifier. I believe that in C++, like C, all identifiers beginning with "str" and followed by a letter are reserved. Say what??????????????? Can you quote chapter and verse from the Holy Standard (or the Holy C standard) on that one? He's not quite got it right. The C standard reserves external symbols that start with str followed by a lower case letter for future use. You can use them internal to a function or class (or other internal linkage) or in a namespace other than std or the global namespace. Back to top Default User Guest Posted: Thu Jan 29, 2004 11:05 pm    Post subject: Re: Converting string to integer Ron Natalie wrote: Quote: He's not quite got it right. The C standard reserves external symbols that start with str followed by a lower case letter for future use. Yes, I forgot to mention the lowercase part. Quote: You can use them internal to a function or class (or other internal linkage) or in a namespace other than std or the global namespace. As far as one could tell from example, it was in the global namespace. 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