Page History

...

Noncompliant code example uses the identifier-list form for parameter declarations.:

int max(a, b)
int a, b;
{
  return a > b ? a : b;
}

...

In this compliant solution, int is the type specifier, max(int a, int b) is the function declarator, and the block within the curly braces is the function body.:

int max(int a, int b) {
  return a > b ? a : b;
}

...

Declaring a function without any prototype forces the compiler to assume that the correct number and type of parameters have been supplied to a function. This practice can result in unintended and undefined behavior.

In this noncompliant code example, the definition of func() in file_a.c expects three parameters but is supplied only two.:

/* file_a.c source file */
int func(int one, int two, int three){
  printf("%d %d %d", one, two, three);
  return 1;
}

However, because there is no prototype for func() in file_b.c, the compiler assumes that the correct number of arguments has been supplied and uses the next value on the program stack as the missing third argument.:

/* file_b.c source file */
func(1, 2);

...

This compliant solution correctly includes the function prototype for func() in the compilation unit in which it is invoked, and the function invocation has been corrected to pass the right number of arguments.:

/* file_b.c source file */
int func(int, int, int);

func(1, 2, 3);

...

To correct this example, the declaration of fn_ptr is changed to accept three arguments.:

int add(int x, int y, int z) {
   return x + y + z;
}

int main(int argc, char *argv[]) {
   int (*fn_ptr) (int, int, int) ;
   int res;
   fn_ptr = add;
   res = fn_ptr(2, 3, 4);
   /* ... */
   return 0;
}

...

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

...

Bibliography

...