C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  String length of command line arguments          C++Talk.NET Forum Index -> C Language (Moderated) View previous topic :: View next topic   Author Message Vinay Guest Posted: Tue May 15, 2007 9:06 pm    Post subject: String length of command line arguments Hello guys, My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. Thanks -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Barry Schwarz Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments On 15 May 2007 16:06:33 GMT, Vinay <samurai1269 (AT) gmail (DOT) com> wrote: Quote: Hello guys, My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. The lower of the two limits: What your C implementation can support (should be documented somewhere) . What your operating system can support (should also be documented somewhere. Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. Why are you copying it? Do you really want to waste all the resources to handle the largest possible argument (which will probably be in the thousands of characters) when it is very unlikely you will ever see anything that long. If you really must copy it, dynamically allocate strlen(argv[1])+1 bytes and use that as your buffer. Remove del for email -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Jonathan Leffler Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments Vinay wrote: Quote: My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. It varies, by platform and the environment. I just had to chop a program that worked OK on Solaris with 128 KB down to 64 KB on Linux to get it to work - 64 KB was the easy number to try when 128 KB failed. -- Jonathan Leffler #include <disclaimer.h> Email: jleffler (AT) earthlink (DOT) net, jleffler (AT) us (DOT) ibm.com Guardian of DBD::Informix v2007.0226 -- http://dbi.perl.org/ -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Douglas A. Gwyn Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments Vinay wrote: Quote: My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? That depends on the platform. It is best not to assume any particular limit. Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. So don't do it that way. Note that argv[i] is a pointer to char, which occupies very little space. You can probably work with that pointer directly. If you do need to allocate storage to hold the pointed-to string, use malloc (and check that it succeeds). -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Gordon Burditt Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments Quote: My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? You pretty much have to assume that it could be near-infinite (e.g. the maximum value of a signed 64-bit number, at least for a few years). In the age of viruses and malware, someone's eventually going to try handing just about any bad argument imaginable to your program. Quote: ex - a.out abcdefghij...................................... What can be the length of that command line argument. Too Long (tm). Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. Then check the length before copying. Or don't use a statically allocated buffer. Or be prepared for trouble when you have to release Service Pack 65536 to fix this, and that just overflowed the 16-bit unsigned number you use to count service packs. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Jack Klein Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments On 15 May 2007 16:06:33 GMT, Vinay <samurai1269 (AT) gmail (DOT) com> wrote in comp.lang.c.moderated: Quote: Hello guys, My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. The C standard does not specify a maximum length for command line arguments. Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. This is entirely platform specific. On some platforms, it is quite possible for a command line argument to be thousands of bytes. There are two possible approaches: 1. Make your buffer the size of the largest string you are willing to accept. At program start up, use strlen() to get the length of argv [1]. If it is larger than your buffer, terminate the program with an error message to the user. 2. If you are not allowed to set a maximum acceptable size, don't allocate the buffer statically. Use strlen() to get the length and then use malloc() to allocate length + 1 bytes. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://c-faq.com/ comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Cumaar Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments Hi Vinay, As far as the command line argument is concerned it thing the max. length of that array should that size of the integer type that particular system (compiler allots) Support the integer is of 32bits then (2^31)-1 This is because the signature says int main(int argc, char *argv[]) {} So if argc is (2^31)-1 you have to provide as many arguments. If i am wrong kindly correct me. Cheers, Kumaar Guhan On May 15, 9:06 pm, Vinay <samurai1...@gmail.com> wrote: Quote: Hello guys, My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. Thanks -- comp.lang.c.moderated - moderation address: c...@plethora.net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Hans-Bernhard Bröker Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments Vinay wrote: Quote: My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? As long as it happens to be. strlen() tells you how long that is. Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. So don't do that then. Use a dynamically allocated buffer, re-think if you really need to copy the argument in order to use it, or just refuse to continue if the argument is too long. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top John Dallman Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments In article <clcm-20070515-0005 (AT) plethora (DOT) net>, samurai1269 (AT) gmail (DOT) com (Vinay) wrote: Quote: My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? This is completely dependent on the operating system you're running on, and quite possibly on other things within that operating system (e.g., on MS-Windows, I seem to remember that COMMAND.COM and CMD.EXE have different limits). If your code is going to try to handle such things portably, a static buffer is the wrong way to do it: use strlen() to find out how big the arguments are and allocate space for them dynamically. -- John Dallman, jgd (AT) cix (DOT) co.uk, HTML mail is treated as probable spam. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Clark Cox Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments On 2007-05-15 09:06:33 -0700, Vinay <samurai1269 (AT) gmail (DOT) com> said: Quote: Hello guys, My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. It can be whatever your platform allows it to be. C really doesn't care. Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. Well, check the length of the argument before copying to the buffer. Or, use a dynamically allocated buffer of the proper size, and be sure to check for NULL return values from malloc and friends. -- Clark S. Cox III clarkcox3 (AT) gmail (DOT) com -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top WillerZ Guest Posted: Thu May 17, 2007 9:11 am    Post subject: Re: String length of command line arguments Vinay wrote: Quote: Hello guys, My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? ex - a.out abcdefghij...................................... What can be the length of that command line argument. System dependant. I've seen up to 32K. Quote: I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. Don't do that then. Use dynamic allocation or, even better, avoid the need to copy the arguments in the first place. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Allan Chandler Guest Posted: Fri May 18, 2007 9:11 am    Post subject: Re: String length of command line arguments Hans-Bernhard Bröker wrote: Quote: Vinay wrote: My question is when we are kicking off a program that expects some arguments ( command line args ), How long can the argument be? As long as it happens to be. strlen() tells you how long that is. I need this because if I am trying to copy argv[1] into a statically allocated buffer it might cause a buffer overflow if I have big command line argument. So don't do that then. Use a dynamically allocated buffer, re-think if you really need to copy the argument in order to use it, or just refuse to continue if the argument is too long. Okay, I've seen plenty of messages suggesting how to do it but none giving a concrete example, which I've always thought would help newbies. I would try something along the lines of: int main (int argc, char *argv[]) { char *argv1copy; if (argc < 2) { fprintf (stderr, "Not enough args\n"); return 1; } argv1copy = malloc (strlen (argv[1]) + 1); if (argv1copy == NULL) { fprintf (stderr, "Cannot allocate memory\n"); return 1; } strcpy (argv1copy, argv[1]); /* Do whatever you have to with argv1copy */ free (argv1copy); return 0; } Most of the posts have been correct on one thing. Unless you need to change the string passed in, you're better off using it where it is rather than making a copy. You can simply put argv1copy = argv[1]; in you code to achieve this. Cheers, Pax -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C Language (Moderated) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.