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# Char * to int

 P: n/a Is it possible to convert char * to integer ? if yes, how to do it ? Jul 22 '05 #1
15 Replies

 P: n/a Kay wrote: Is it possible to convert char * to integer ? if yes, how to do it ? char const * z = "12"; stringstream stream = z; int q = 0; if (z >> q) cout << "yes" << endl; (strtol() also works.) -- Phlip http://industrialxp.org/community/bi...UserInterfaces Jul 22 '05 #2

 P: n/a "Kay" wrote in message news:41**************@yahoo.com.hk... Is it possible to convert char * to integer ? No, not portably. if yes, how to do it ? Perhaps you want to convert the textual representation of a number to an integer type. If so, use a stringstream. #include #include int main() { const char *x = "123"; std::istringstream iss(x); int i(0); if(iss >> i) std::cout << i << '\n'; else std::cerr << "unable to convert\n"; return 0; } -Mike Jul 22 '05 #3

 P: n/a "Kay" wrote in message news:41**************@yahoo.com.hk... Is it possible to convert char * to integer ? if yes, how to do it ? The technique listed in the FAQ for converting std::strings to numbers will also work for C-style strings. See the FAQ (http://www.parashift.com/c++-faq-lite/), section 38 ("Miscellaneous technical issues"), question 2 ("How do I convert a std::string to a number?"). -- David Hilsee Jul 22 '05 #4

 P: n/a "Phlip" wrote in message news:Nj******************@newssvr17.news.prodigy.c om... Kay wrote: Is it possible to convert char * to integer ? if yes, how to do it ? char const * z = "12"; stringstream stream = z; int q = 0; if (z >> q) cout << "yes" << endl; (strtol() also works.) -- Phlip http://industrialxp.org/community/bi...UserInterfaces Isn't using 'atoi' function in much simpler? Jul 22 '05 #5

 P: n/a Method Man wrote: > Is it possible to convert char * to integer ? > if yes, how to do it ? char const * z = "12"; stringstream stream = z; int q = 0; if (z >> q) cout << "yes" << endl; (strtol() also works.) Isn't using 'atoi' function in much simpler? Yes, but it's also much worse, because it has a design bug. It doesn't provide any way to find out whether the conversion was successful. Jul 22 '05 #6

 P: n/a "Method Man" wrote in message news:1L*********************@read2.cgocable.net... "Phlip" wrote in message news:Nj******************@newssvr17.news.prodigy.c om... Kay wrote: Is it possible to convert char * to integer ? if yes, how to do it ? char const * z = "12"; stringstream stream = z; int q = 0; if (z >> q) cout << "yes" << endl; (strtol() also works.) -- Phlip http://industrialxp.org/community/bi...UserInterfaces Isn't using 'atoi' function in much simpler? Yes, but it cannot be used safely. (Does not protect from overflow, which would cause undefined behavior. Also, a valid result of zero cannot be distinguished from an error, which 'atoi()' indicates by returning zero. -Mike Jul 22 '05 #7

 P: n/a Method Man wrote: "Phlip" wrote in message news:Nj******************@newssvr17.news.prodigy.c om... Kay wrote: Is it possible to convert char * to integer ? if yes, how to do it ? char const * z = "12"; stringstream stream = z; int q = 0; if (z >> q) cout << "yes" << endl; (strtol() also works.) -- Phlip http://industrialxp.org/community/bi...rstUserInterfa ces Isn't using 'atoi' function in much simpler? Simpler, perhaps. It has no error handling capability though. It's generally recommended to you strtol() if you want to use C-style functionality. Brian Rodenborn Jul 22 '05 #8

 P: n/a "Mike Wahler" wrote in message news:f6*****************@newsread1.news.pas.earthl ink.net... "Method Man" wrote in message news:1L*********************@read2.cgocable.net... "Phlip" wrote in message news:Nj******************@newssvr17.news.prodigy.c om... Kay wrote: > Is it possible to convert char * to integer ? > if yes, how to do it ? char const * z = "12"; stringstream stream = z; int q = 0; if (z >> q) cout << "yes" << endl; (strtol() also works.) -- Phlip http://industrialxp.org/community/bi...UserInterfaces Isn't using 'atoi' function in much simpler? Yes, but it cannot be used safely. (Does not protect from overflow, which would cause undefined behavior. Also, a valid result of zero cannot be distinguished from an error, which 'atoi()' indicates by returning zero. -Mike Hmm, I would just write my own version of 'atoi' then. At the least, it's good practice for a C/C++ job interview. ;) Jul 22 '05 #9

 P: n/a "Method Man" wrote in message news:76*****************@read1.cgocable.net... "Mike Wahler" wrote in message news:f6*****************@newsread1.news.pas.earthl ink.net... "Method Man" wrote in message news:1L*********************@read2.cgocable.net... "Phlip" wrote in message news:Nj******************@newssvr17.news.prodigy.c om... > > (strtol() also works.) Isn't using 'atoi' function in much simpler? Yes, but it cannot be used safely. (Does not protect from overflow, which would cause undefined behavior. Also, a valid result of zero cannot be distinguished from an error, which 'atoi()' indicates by returning zero. -Mike Hmm, I would just write my own version of 'atoi' then. At the least, it's good practice for a C/C++ job interview. ;) Why would you not use 'strto(u)l()'? If a candidate wasted time reinventing what the standard library already has, I would not be impressed. I'd be more impressed with one who knows which tools are available, and when/how/where to apply them. Anyone familiar with C or C++ will recognize 'strtol()' at a glance, whereas upon encountering a 'home-grown' conversion function, one would need to find out what the darn thing actually does. Also, a standard library function has a far better chance of being fully debugged and robust. -Mike Jul 22 '05 #10

 P: n/a Kay wrote: Is it possible to convert char * to integer ? if yes, how to do it ? int main(int argc, char * argv[]) { using boost::lexical_cast; using boost::bad_lexical_cast; std::vector args; while(*++argv) { try { args.push_back(lexical_cast(*argv)); } catch(bad_lexical_cast &) { args.push_back(0); } } ... } There you go... Jul 22 '05 #11

 P: n/a "Mike Wahler" wrote in message news:qg****************@newsread1.news.pas.earthli nk.net... "Method Man" wrote in message news:76*****************@read1.cgocable.net... "Mike Wahler" wrote in message news:f6*****************@newsread1.news.pas.earthl ink.net... "Method Man" wrote in message news:1L*********************@read2.cgocable.net... > > "Phlip" wrote in message > news:Nj******************@newssvr17.news.prodigy.c om... > > > (strtol() also works.) Isn't using 'atoi' function in much simpler? Yes, but it cannot be used safely. (Does not protect from overflow, which would cause undefined behavior. Also, a valid result of zero cannot be distinguished from an error, which 'atoi()' indicates by returning zero. -Mike Hmm, I would just write my own version of 'atoi' then. At the least, it's good practice for a C/C++ job interview. ;) Why would you not use 'strto(u)l()'? If a candidate wasted time reinventing what the standard library already has, I would not be impressed. I'd be more impressed with one who knows which tools are available, and when/how/where to apply them. Anyone familiar with C or C++ will recognize 'strtol()' at a glance, whereas upon encountering a 'home-grown' conversion function, one would need to find out what the darn thing actually does. Also, a standard library function has a far better chance of being fully debugged and robust. -Mike Yes, you're right. I guess I've always used 'atoi'. This is what I was taught back in my 1st year university CS class for converting any C-style strings to int. Regarding the interview question. I've actually been asked to specifically implement 'atoi' in two separate interviews. I suppose the context was simply that it's a good test for one's pointer knowledge and error handling ability with strings. Jul 22 '05 #12

 P: n/a Method Man wrote: I guess I've always used 'atoi'. This is what I was taught back in my 1st year university CS class for converting any C-style strings to int. Regarding the interview question. I've actually been asked to specifically implement 'atoi' in two separate interviews. I suppose the context was simply that it's a good test for one's pointer knowledge and error handling ability with strings. int atoi( char* String ) { int Result; sscanf( "%d", Result ); return Result; } :-) I guess this is not what your interviewer expected you to do :-) -- Karl Heinz Buchegger kb******@gascad.at Jul 22 '05 #13

 P: n/a "Karl Heinz Buchegger" wrote in message news:41***************@gascad.at... Method Man wrote: I guess I've always used 'atoi'. This is what I was taught back in my 1st year university CS class for converting any C-style strings to int. Regarding the interview question. I've actually been asked to specifically implement 'atoi' in two separate interviews. I suppose the context was simply that it's a good test for one's pointer knowledge and error handling ability with strings. int atoi( char* String ) { int Result; sscanf( "%d", Result ); return (sscanf(String, "%d", &Result) == 1) ? Result : 0; return Result; } -Mike Jul 22 '05 #14

 P: n/a Method Man wrote: Hmm, I would just write my own version of 'atoi' then. At the least, it's good practice for a C/C++ job interview. ;) If asked to write atoi() at a job interview, I would match its exact ISO specification, verbally point out all its minor flaws, reveal when and when not I would use it, and write wrapper code that defends its calls. (Not sure if I could match the performance with lexical_cast, though!) -- Phlip http://industrialxp.org/community/bi...UserInterfaces Jul 22 '05 #15

 P: n/a Phlip wrote: Method Man wrote: Hmm, I would just write my own version of 'atoi' then. At the least, it's good practice for a C/C++ job interview. ;) If asked to write atoi() at a job interview, I would match its exact ISO specification, verbally point out all its minor flaws, It has minor flaws too? reveal when and when not I would use it, and write wrapper code that defends its calls. If asked to write it, I'd write it. Nothing more. If they want to know more, they can ask. Well, maybe I'd just note that atoi() is a bad idea because has a major design bug. It's just like in oral exams. Don't answer questions that have not been asked. Jul 22 '05 #16

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