CODEWITHSUNDEEP
c++cgccprintfvariadic-functions
rsk82
rsk82

Reputation: 29407

what's the cause of this difference when encapsulating printf and vfprintf with another function?

In this example this code although compiles it doesn't produce correct result:

void encapsulatePrintf(const char *str, ...) {
  va_list argptr;
  va_start(argptr, str);
  printf(str, argptr);
  va_end(argptr);
}

and then in main: encapsulatePrintf("test str: %i - %s", 22, "test2");

but when I change the function from printf to vfprintf(stdout, str, argptr);

What's going on here ?

Upvotes: 3

Views: 175

Answers (1)

Dietmar Kühl
Dietmar Kühl

Reputation: 154025

printf() doesn't take va_list as argument but rather a variable list of arguments while vprintf() takes a va_list as argument and not a variable list of arguments. Basically, when you called printf() using

printf(str, argptr);

you invoked undefined behavior: the first argument promised that you would pass an int and a char* but you passed, instead, a va_list. The types of the arguments passed to printf() have to match the specification in the format string.

Upvotes: 8

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