How should I print types like off t and size t

Question

I m trying to print types like off t and size t   What is the correct placeholder for printf   that is portable   Or is there a completely different way to print those variables

User · Answer

To print off t   printf   jd n    intmax t x     To print size t   printf   zu n   x     To print ssize t   printf   zd n   x     See 7 19 6 1 7 in the C99 standard  or the more convenient POSIX documentation of formatting codes   http   pubs opengroup org onlinepubs 009695399 functions fprintf html  If your implementation doesn t support those formatting codes  for example because you re on C89   then you have a bit of a problem since AFAIK there aren t integer types in C89 that have formatting codes and are guaranteed to be as big as these types  So you need to do something implementation-specific   For example if your compiler has long long and your standard library supports  lld  you can confidently expect that will serve in place of intmax t  But if it doesn t  you ll have to fall back to long  which would fail on some other implementations because it s too small

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You ll want to use the formatting macros from inttypes h   See this question   Cross platform format string for variables of type size t

User · Answer

Which version of C are you using   In C90  the standard practice is to cast to signed or unsigned long  as appropriate  and print accordingly   I ve seen  z for size t  but Harbison and Steele don t mention it under printf    and in any case that wouldn t help you with ptrdiff t or whatever   In C99  the various  t types come with their own printf macros  so something like  Size is   FOO   bytes    I don t know details  but that s part of a fairly large numeric format include file

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For Microsoft  the answer is different   VS2013 is largely C99 compliant but   t he hh  j  z  and t length prefixes are not supported   For size t  that is  unsigned   int32 on 32-bit platforms  unsigned   int64 on 64-bit platforms  use prefix I  capital eye  with type specifier o  u  x  or X   See VS2013 Size specification  As for off t  it is defined as long in VC include sys types h

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As I recall  the only portable way to do it  is to cast the result to  unsigned long int  and use  lu   printf  sizeof int     lu    unsigned long  sizeof int

User · Answer

I saw this post at least twice  because the accepted answer is hard to remeber for me I rarely use z or j flags and they are seems not platform independant     The standard never says clearly the exact data length of size t  so I suggest you should first check the length size t on your platform then select one of them   if sizeof size t     4 use PRIu32 if sizeof size t     8 use PRIu64   And I suggest using stdint types instead of raw data types for consistancy

User · Answer

You can use z for size t and t for ptrdiff t like in  printf   zu  td   size  ptrdiff     But my manpage says some older library used a different character than z and discourages use of it  Nevertheless  it s standardized  by the C99 standard   For those intmax t and int8 t of stdint h and so on  there are macros you can use  like another answer said   printf  value     PRId32  some int32 t   printf  value     PRIu16  some uint16 t     They are listed in the manpage of inttypes h    Personally  I would just cast the values to unsigned long or long like another answer recommends  If you use C99  then you can  and should  of course  cast to unsigned long long or long long and use the  llu or  lld formats respectively

User · Answer

use   zo  for off t   octal  or   zu  for decimal

User · Answer

Looking at man 3 printf on Linux  OS X  and OpenBSD all show support for  z for size t and  t for ptrdiff t  for C99   but none of those mention off t  Suggestions in the wild usually offer up the  u conversion for off t  which is  correct enough  as far as I can tell  both unsigned int and off t vary identically between 64-bit and 32-bit systems

[c] How should I print types like off_t and size_t?

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