CODEWITHSUNDEEP
gccclangcompiler-warningsgcc-warning
gil_mo
gil_mo

Reputation: 625

GCC Compiler options -wno-four-char-constants and -wno-multichar

Couldn't find any documentation on -Wno-four-char-constants, however I suspect that it is similar to -Wno-multichar. Am I correct?

Upvotes: 5

Views: 2252

Answers (1)

manlio
manlio

Reputation: 18962

They're related but not the same thing.

Compiling with the -Wall --pedantic flags, the assignment:

int i = 'abc';

produces:

warning: multi-character character constant [-Wmultichar]

with both GCC and CLANG, while:

 int i = 'abcd';

produces:

GCC warning: multi-character character constant [-Wmultichar]

CLANG warning: multi-character character constant [-Wfour-char-constants]

The standard (C99 standard with corrigenda TC1, TC2 and TC3 included, subsection 6.4.4.4 - character constants) states that:

The value of an integer character constant containing more than one character (e.g., 'ab'), [...] is implementation-defined.

A multi-char always resolves to an int but, since the order in which the characters are packed into one int is not specified, portable use of multi-character constants is difficult (the exact value is implementation-dependent).

Also compilers differ in how they handle incomplete multi-chars (such as 'abc').

Some compilers pad on the left, some on the right, regardless of endian-ness (some compilers may not pad at all).

Someone who can accept the portability problems of a complete multi-char may anyway want a warning for an incomplete one (-Wmultichar -Wno-four-char-constants).

Upvotes: 6

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