Synopsis

Do not call va_arg with an argument of the incorrect type

Enabled by default

Yes

Severity/Certainty

Medium/Medium

Full description

Ensure that an invocation of the va_arg() macro does not attempt to access an argument that was not passed to the variadic function. Further, the type passed to the va_arg() macro must match the type passed to the variadic function after default argument promotions have been applied.

Coding standards

This check does not correspond to any coding standard rules.

Code examples

The following code example fails the check and will give a warning:

#include <stdarg.h>

void func(const char *cp, ...) {
  va_list ap;
  va_start(ap, cp);
  int val = va_arg(ap, int);
  // ...
  va_end(ap);
}

void f(void) {
  func("The only argument");
}

The following code example passes the check and will not give a warning about this issue:

#include <stdarg.h>
#include <stddef.h>

void func(size_t num_vargs, const char *cp, ...) {
  va_list ap;
  va_start(ap, cp);
  if (num_vargs > 0) {
    int val = va_arg(ap, int);
    // ...
  }
  va_end(ap);
}

void f(void) {
  func(0, "The only argument");
}