The parameters of a variadic function are interpreted by the va_arg() macro. The va_arg() macro is used to extract the next argument from an initialized argument list within the body of a variadic function implementation. The size of each parameter is determined by the specified type. If type is inconsistent with the corresponding argument, the behavior is undefined and may result in misinterpreted data or an alignment error (see EXP36-C. Do not cast between pointers between objects or types with differing alignments) could result.
Because arguments to variadic functions are untyped, the programmer is responsible for ensuring that arguments to variadic functions are of the same type as the corresponding parameter except for the following cases:
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The C99 printf() function is implemented as a variadic functionsfunction. This non-compliant code example swaps its null terminated byte string and integer parameters with respect to how they were specified in the format string. Consequently, the integer is silently converted into a pointer to a null terminated byte string and then dereferenced, possibly causing the program to abnormally terminate (error_message pointer is likewise silently converted into an integer).
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