CODEWITHSUNDEEP
ccompiler-warningsformat-specifiersstdint
opisthofulax
opisthofulax

Reputation: 551

Format specifier in <inttypes.h> causes warning in cross-platform compatibility

I am using library <inttypes.h> (<stdint.h>) for compatibility across platforms in usigned types. When compiling on my MacOSX with -Wall options no warnings arise, while on Ubuntu 20.04 I get

mvmpi.c: In function ‘main’:
mvmpi.c:33:9: warning: format ‘%u’ expects argument of type ‘unsigned int *’, but argument 6 has type ‘uint16_t *’ {aka ‘short unsigned int *’} [-Wformat=]
   33 |         "%"PRIu32"%"PRIu32"%lf%"PRIu16, &N, &M, &L, &SN) != EOF) {
      |         ^~~                                         ~~~
      |                                                     |
      |                                                     uint16_t * {aka short unsigned int *}
In file included from stdbasic.h:33,
                 from mvmpilib.h:8,
                 from mvmpi.c:4:
/usr/include/inttypes.h:103:19: note: format string is defined here
  103 | # define PRIu16  "u"

The formatting complains about variable SN which is declared to be uint16_t variable and then it uses "%"PRIu16 format specifier, but surprisingly it appears that PRIu16 is defined in C sources libraries as unsigned int, while uint16_t would be (regularly) short unsigned int.

What is going on here? How to solve and mantain cross platform compatibility? Of course uint16_t from documentation is defined with at least 16 bits, but if the format specifier is more, then also it must be bigger in order to maintain coherence.

Upvotes: 0

Views: 365

Answers (1)

MikeCAT
MikeCAT

Reputation: 75062

PRIu16 is for printing uint16_t.

You have to use SCNu16 for reading uint16_t.

Also you have to use SCNu32, not PRIu32, for reading uint32_t.

Upvotes: 4

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