Multi-character constant warnings

Question

Why is this a warning  I think there are many cases when is more clear to use multi-char int constants instead of  no meaning  numbers or instead of defining const variables with same value  When parsing wave tiff other file types is more clear to compare the read values with some  EVAW    data   etc instead of their corresponding values   Sample code   int waveHeader    EVAW     Why does this give a warning

User · Answer

If you re happy you know what you re doing and can accept the portability problems  on GCC for example you can disable the warning on the command line   -Wno-multichar   I use this for my own apps to work with AVI and MP4 file headers for similar reasons to you

User · Answer

According to the standard    6 4 4 4 10      The value of an integer character constant containing more than one   character  e g    ab          is implementation-defined    long x     xde xad xbe xef      yes  single quotes   This is valid ISO 9899 2011 C   It compiles without warning under gcc with -Wall  and a    multi-character character constant    warning with -pedantic   From Wikipedia      Multi-character constants  e g   xy   are valid  although rarely   useful     they let one store several characters in an integer  e g  4   ASCII characters can fit in a 32-bit integer  8 in a 64-bit one     Since the order in which the characters are packed into one int is not   specified  portable use of multi-character constants is difficult    For portability sake  don t use multi-character constants with integral types

User · Answer

This warning is useful for programmers that would mistakenly write  test  where they should have written  test    This happen much more often than programmers that do actually want multi-char int constants

User · Answer

If you want to disable this warning it is important to know that there are two related warning parameters in GCC and Clang  GCC Compiler options -wno-four-char-constants and -wno-multichar

User · Answer

Simplest C C   any compiler standard compliant solution  was mentioned by  leftaroundabout in comments above   int x     int   abcd     Or a bit more specific   int x     int32 t   abcd     One more solution  also compliant with C C   compiler standard since C99  except clang    which has a known bug    int x     union  char s 5   int number     abcd    number      just a demo check     printf  x  d stored  s byte first n   x  x  0x61626364    MSB   LSB      Here anonymous union is used to give a nice symbol-name to the desired numeric result   abcd  string is used to initialize the lvalue of compound literal  C99

User · Answer

Even if you re willing to look up what behavior your implementation defines  multi-character constants will still vary with endianness   Better to use a  POD  struct   char 4          and then use a UDL like  WAVE  4cc to easily construct instances of that class

[c++] Multi-character constant warnings

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