C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Confused in function: close() and bzero()          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Charles Guest Posted: Mon Sep 20, 2004 3:34 pm    Post subject: Confused in function: close() and bzero() I am a newbie recently starting some network programming practices using GCC. I noticed some strange things while compiling the code below. **************************************** #include <stdio.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> char * host_name = "127.0.0.1"; int port = 8000; void main(int argc, char *argv[]) { int socket_descriptor; struct sockaddr_in pin; .... bzero(&pin, sizeof(pin)); .... socket_descriptor = socket(AF_INET, SOCK_STREAM, 0) .... close(socket_descriptor); } ************************ It's quoted from a sample client program. When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? My machine is redhat 8.0 kernel 2.4, gcc version is 3.2. Could somebody explain it to me? Thanks a lot. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Felipe Magno de Almeida Guest Posted: Tue Sep 21, 2004 11:26 am    Post subject: Re: Confused in function: close() and bzero() Charles wrote: Quote: I am a newbie recently starting some network programming practices using GCC. I noticed some strange things while compiling the code below. **************************************** #include <stdio.h #include #include #include #include char * host_name = "127.0.0.1"; int port = 8000; void main(int argc, char *argv[]) { int socket_descriptor; struct sockaddr_in pin; ... bzero(&pin, sizeof(pin)); ... socket_descriptor = socket(AF_INET, SOCK_STREAM, 0) ... close(socket_descriptor); } ************************ It's quoted from a sample client program. When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? include them #include #include <unistd.h> in C, you can use the function without defining it anywhere, but in C++ it is completly prohibited. -- Felipe Magno de Almeida UIN: 2113442 email: felipe.almeida@ic unicamp br, felipe.m.almeida@gmail com I am a C, modern C++, MFC, ODBC, Windows Services, MAPI developer from synergy, and Computer Science student from State University of Campinas(UNICAMP). To know more about: Unicamp: http://www.ic.unicamp.br Synergy: http://www.synergy.com.br current work: http://www.mintercept.com [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Nicolas Pavlidis Guest Posted: Tue Sep 21, 2004 11:29 am    Post subject: Re: Confused in function: close() and bzero() [email]charling_us (AT) hotmail (DOT) com[/email] (Charles) writes: Quote: I am a newbie recently starting some network programming practices using GCC. I noticed some strange things while compiling the code below. **************************************** #include #include #include #include #include char * host_name = "127.0.0.1"; int port = 8000; void main(int argc, char *argv[]) { int main(..) please ... :-) [snipp] Quote: It's quoted from a sample client program. When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? That's because gcc links automatically the hole C - Library, including string.h and so on, but g++ (the C++ - frontend) doesn't do this. Trye to compile the code with gcc withOption -Wall and you'll get some warnings that some function aren't declared. HTH && Kind regards, Nicolas -- Quote: Nicolas Pavlidis | Elvis Presly: | |__ | Student of SE & KM | "Into the goto" | |__| | [email]pavnic (AT) sbox (DOT) tugraz.at[/email] | ICQ #320057056 | | -------------------University of Technology, Graz----------------| [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Victor Bazarov Guest Posted: Tue Sep 21, 2004 11:33 am    Post subject: Re: Confused in function: close() and bzero() Charles wrote: Quote: I am a newbie recently starting some network programming practices using GCC. I noticed some strange things while compiling the code below. **************************************** #include <stdio.h #include #include #include #include char * host_name = "127.0.0.1"; int port = 8000; void main(int argc, char *argv[]) { int socket_descriptor; struct sockaddr_in pin; ... bzero(&pin, sizeof(pin)); ... socket_descriptor = socket(AF_INET, SOCK_STREAM, 0) ... close(socket_descriptor); } ************************ It's quoted from a sample client program. When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? My machine is redhat 8.0 kernel 2.4, gcc version is 3.2. Could somebody explain it to me? Thanks a lot. Setting aside the fact that 'bzero' and 'close' are not standard C functions, your question can still be answered with, "probably because those headers [that are not directly included in the given source] do nonetheless get included [indirectly, by other headers used here]". Since four out of five headers in the posted code are non-standard, there is nothing that can be said about what they themselves include when preprocessed. Try outputting the result of preprocessor work, and you can see for yourself who includes the "missing" headers, Oh, BTW, 'main' is supposed to return 'int'. Victor [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jack Klein Guest Posted: Tue Sep 21, 2004 11:34 am    Post subject: Re: Confused in function: close() and bzero() On 20 Sep 2004 11:34:32 -0400, [email]charling_us (AT) hotmail (DOT) com[/email] (Charles) wrote in comp.lang.c++.moderated: Quote: I am a newbie recently starting some network programming practices using GCC. Neither network programming nor GCC are appropriate here. The C++ language standard does not define any networking support at all, nor does it define the specifics of using specific compilers and linkers. Quote: I noticed some strange things while compiling the code below. **************************************** #include <stdio.h #include #include #include #include char * host_name = "127.0.0.1"; int port = 8000; void main(int argc, char *argv[]) { Both C and C++ require that main() be defined with a return type of int. Neither language takes any responsibility for the results of a program that begins with "void main". Quote: int socket_descriptor; struct sockaddr_in pin; ... bzero(&pin, sizeof(pin)); ... socket_descriptor = socket(AF_INET, SOCK_STREAM, 0) ... close(socket_descriptor); } ************************ It's quoted from a sample client program. When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? My machine is redhat 8.0 kernel 2.4, gcc version is 3.2. Could somebody explain it to me? Thanks a lot. Neither 'close' nor 'bzero' is a standard C++ library function. These, along all of the headers except for extensions provided by your compiler/operating system combination. You need to ask this question in a one of the GCC support groups, or a Linux programming group like news:comp.os.linux.development.apps. It is not a C++ language issue at all. -- 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 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Ulrich Eckhardt Guest Posted: Tue Sep 21, 2004 11:35 am    Post subject: Re: Confused in function: close() and bzero() Charles wrote: Quote: It's quoted from a sample client program. When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. The language C allows functions to be used without them being declared, in C++ that constitutes an error. Nonetheless, it can still invoke undefined behaviour in C if the assumed prototype doesn't match the actual function's declaration, which is why even in C it is frowned upon. Specific to GCC's C and C++ compilers is the commandline flag '-Wall' which you should always use. It would have warned yuo about the dubious use in the C case. Use of gcc or g++ is rather off-topic here though, for questions consult the gnu.*.help groups. cheers Uli -- FAQ: http://parashift.com/c++-faq-lite/ /* bittersweet C++ */ default: break; [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Tue Sep 21, 2004 11:48 am    Post subject: Re: Confused in function: close() and bzero() [email]charling_us (AT) hotmail (DOT) com[/email] (Charles) wrote in message news:<4d10c1c8.0409192202.1c061282 (AT) posting (DOT) google.com>... Quote: I am a newbie recently starting some network programming practices using GCC. I noticed some strange things while compiling the code below. **************************************** #include <stdio.h #include #include #include #include char * host_name = "127.0.0.1"; In C++, we'd almost certainly write "char const*', rather than "char*". In both C and C++, I'd use an array, rather than a pointer. In C++, of course, I'd almost certainly use std::string. And of course, in a real program, this sort of thing wouldn't be a global. Quote: int port = 8000; void main(int argc, char *argv[]) { Technically, "void main" is illegal in both C and C++. Practically, it is widely used under Windows, but some Unix compilers (including up to date versions of gcc) correctly reject it. Quote: int socket_descriptor; struct sockaddr_in pin; ... bzero(&pin, sizeof(pin)); This is NOT a standard C/C++ function. Use memset. Quote: ... socket_descriptor = socket(AF_INET, SOCK_STREAM, 0) ... close(socket_descriptor); } ************************ It's quoted from a sample client program. I don't know where you got the sample, but it isn't what I would call a good example. Quote: When I compiled it using gcc (which is supposed to be C complier, is it right?), it's OK. But when I try using g++ to compile it, it always reports that close() and bzero() are not declared. First, whether gcc compiles code as C or as C++ depends on the source filename, not whether it is invoked as gcc or as g++. The invocation controls which libraries are implicitly linked (so linking C++ code with gcc will generally result in undefined externals), and possibly where it looks for headers. Secondly, there is NO standard function, either in C or in C++, by the name of bzero. In is present in Posix, but it is documented there as a legacy function, which should not be used in new code. According to Posix, the header which contains it is You should replace it with memset (in <string.h>). With regards to close, it is also not a C or a C++ function. It is a Posix function, however, and it should be defined in <unistd.h>. Which you don't include. Quote: Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? In C, functions may be declared implicitly. This is a deprecated feature in the latest version of the C standard, so ideally, you should get a warning. Try compiling with -Wmissing-prototypes (and don't ask me why this one isn't in -Wall). In general, I've yet to find a compiler whose default options are useful. Gcc is no exception. Read the documentation, and define the options you need. (The exact list of options will depend on the application. But -Wmissing-prototypes should definitly be in there, at least when compiling C.) Quote: My machine is redhat 8.0 kernel 2.4, gcc version is 3.2. And it accepts "void main"? Quote: Could somebody explain it to me? Thanks a lot. Just one of the differences between C and C++. And a good reason why you should probable steer clear of C, even if you don't want all of the features of C++. -- James Kanze GABI Software http://www.gabi-soft.fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Wed Sep 22, 2004 9:54 am    Post subject: Re: Confused in function: close() and bzero() Jack Klein <jackklein (AT) spamcop (DOT) net> wrote Quote: On 20 Sep 2004 11:34:32 -0400, [email]charling_us (AT) hotmail (DOT) com[/email] (Charles) wrote in comp.lang.c++.moderated: I am a newbie recently starting some network programming practices using GCC. Neither network programming nor GCC are appropriate here. The C++ language standard does not define any networking support at all, nor does it define the specifics of using specific compilers and linkers. but his problem has nothing to do with either. Quote: I noticed some strange things while compiling the code below. **************************************** #include <stdio.h #include #include #include #include char * host_name = "127.0.0.1"; int port = 8000; void main(int argc, char *argv[]) { Both C and C++ require that main() be defined with a return type of int. Neither language takes any responsibility for the results of a program that begins with "void main". C++ does: it says that the compiler must emit a diagnostic. Another poster said simply "int main(..) please". In this particular case, it is more than please. The poster is compiling with g++, and current versions of g++ do conform to the standard in this regard. The code won't compile with void main. [...] Quote: Neither 'close' nor 'bzero' is a standard C++ library function. But his question didn't concern anything specific to close or bzero. His question was basically, why the code compiled in C and not in C++. Quote: These, along all of the headers except for extensions provided by your compiler/operating system combination. You need to ask this question in a one of the GCC support groups, or a Linux programming group like news:comp.os.linux.development.apps. It is not a C++ language issue at all. It actually is, more or less. It concerns a major difference between C and C++: the fact that functions may be implicitly declared in C, but not in C++. Most C compilers warn when they encounter an implicitly declared function. Of course, you do have to turn on warnings (-Wall for gcc/g++). -- James Kanze GABI Software http://www.gabi-soft.fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Sebastian Kapfer Guest Posted: Thu Sep 23, 2004 8:18 am    Post subject: Re: Confused in function: close() and bzero() On Tue, 21 Sep 2004 07:29:36 -0400, Nicolas Pavlidis wrote: Quote: charling_us (AT) hotmail (DOT) com (Charles) writes: Also after researching "man close", I found close() is included in "unistd.h" and by "man bzero", I found bzero() is included in "string.h". But both "string.h" and "unistd.h" are not included in the above code. How can it pass the compiling? That's because gcc links automatically the hole C - Library, including string.h and so on, but g++ (the C++ - frontend) doesn't do this. g++ also links the whole C library. The important difference is that g++ is a C++ compiler and thus rejects calls to functions without prototypes. That's basically what an #include does, it declares function prototypes (and other stuff). #include has nothing to do with linking. -- Best Regards, | I couldn't afford a cool signature, Sebastian | so I just got this one. Quote: -------------------------------------------------------- mailbox in "From" silently drops any mail > 20k [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Old Wolf Guest Posted: Sat Sep 25, 2004 5:36 pm    Post subject: Re: Confused in function: close() and bzero() [email]kanze (AT) gabi-soft (DOT) fr[/email] wrote: Quote: charling_us (AT) hotmail (DOT) com (Charles) wrote: char * host_name = "127.0.0.1"; In C++, we'd almost certainly write "char const*', rather than "char*". In both C and C++, I'd use an array, rather than a pointer. Why? In practical terms, I would prefer the pointer, based on the following logic: "127.0.0.1" exists in the string table. Pointing to it requires 4 bytes, whereas declaring an automatic array involves copying 10 bytes (ie. slower). I would only be keen on copying an object if one of the copies had to be modified. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Mon Sep 27, 2004 8:15 pm    Post subject: Re: Confused in function: close() and bzero() [email]oldwolf (AT) inspire (DOT) net.nz[/email] (Old Wolf) wrote in message news:<843a4f78.0409231818.34d015db (AT) posting (DOT) google.com>... Quote: kanze (AT) gabi-soft (DOT) fr wrote: [email]charling_us (AT) hotmail (DOT) com[/email] (Charles) wrote: char * host_name = "127.0.0.1"; In C++, we'd almost certainly write "char const*', rather than "char*". In both C and C++, I'd use an array, rather than a pointer. Why? Habit. In C, the array could be const char[], where as a string literal is char[], so a possible source of errors is eliminated. Quote: In practical terms, I would prefer the pointer, based on the following logic: "127.0.0.1" exists in the string table. What string table? Quote: Pointing to it requires 4 bytes, whereas declaring an automatic array involves copying 10 bytes (ie. slower). I would only be keen on copying an object if one of the copies had to be modified. I very much doubt that the array would be automatic. When I declare a const object in block scope, it is almost an automatism to declare it static. If the object has static lifetime, then declaring a pointer takes four extra bytes, plus an extra indirection for every access. -- James Kanze GABI Software http://www.gabi-soft.fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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