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C: difference between snprintf and smprintf?
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LoTeK
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Joined: 26 Jul 2012
Posts: 270

PostPosted: Fri Feb 01, 2013 10:20 am    Post subject: C: difference between snprintf and smprintf? Reply with quote

hi,
In the helper functions of dwm http://dwm.suckless.org/dwmstatus/ there is used a function called: smprintf But google returns way more information on snprintf and less to nothing about smprintf.

If I'm playing around with those helper functions I always get the error:
Code:
undefined reference to smprintf


If I just replace all smprintfs with snprintfs I'll get:
Code:
to few arguments to function snprintf


I'm reading the very good book "Topics in C programming" at the moment, but although many functions are discussed, smprintf isn't mentioned.
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Genone
Retired Dev
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Joined: 14 Mar 2003
Posts: 9004
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PostPosted: Fri Feb 01, 2013 10:24 am    Post subject: Reply with quote

Never heard about smprintf, so I assume it's simply a helper function those guys wrote themselves.
EDIT: Google listed https://github.com/apgwoz/dwm/blob/master/dwmstatus.c as a result for smprintf, which defines smprintf simply as a version of snprintf that determines the output string length and allocates the output buffer itself. Convenient, but lots of potential for memory leaks.
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Hu
Watchman
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Joined: 06 Mar 2007
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PostPosted: Sat Feb 02, 2013 1:30 am    Post subject: Reply with quote

I concur with regard to memory leaks. If you can assume the use of _GNU_SOURCE, then glibc provides asprintf, with similar functionality, but a prototype that is slightly less prone to leaks. Otherwise, stick with snprintf. In most cases, if you cannot predict the size of the output buffer, allowing an automatically sized buffer is a bad choice.
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