Why Do Multi-Character Constants in C Cause Warnings and How Can They Be Avoided?

Multi-Character Constant Warnings in C

In C, multi-character constant warnings are issued when an integer constant contains more than one character. Consider the following code:

int waveHeader = 'EVAW';

This code will generate a warning because the integer constant 'EVAW' contains four characters.

According to the C standard (§6.4.4.4/10), the value of a multi-character integer constant is implementation-defined. This means that different compilers may interpret the constant differently. For example, the following code may compile without warning on one compiler and with a warning on another:

long x = '\xde\xad\xbe\xef';

To avoid potential portability issues, it is recommended not to use multi-character constants with integral types. Instead, consider using "no meaning" numbers or defining const variables with the same value.

For example, the following code would be more portable than the example above:

#define EVAW 'EVAW'
int waveHeader = EVAW;

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