Call functions with the correct arguments

Calling a function with incorrect arguments can result in unexpected or unintended program behavior. Functions that are appropriately declared [[DCL07-A. Include the appropriate type information in function declarators]] will fail compilation if they are supplied with the wrong number or types of arguments. However, there are cases where supplying the incorrect arguments to a function will only generate compiler warnings. These warnings should be resolved [[MSC00-A. Compile cleanly at high warning levels]], but do not prevent program compilation.

Non-Compliant Code Example: (function pointers)

In this example, the function pointer fp is used to refer to the function strchr(). However, fp is defined without the appropriate parameter list. As a result there is no type checking performed on the call to fp(12,2);.

#include <stdio.h>
#include <string.h>

char *(*fp) ();

int main(void) {
  char *c;
  fp = strchr;
  c = fp(12,2);
  printf("%s\n",c);

}

Note that this example also violates recommendation [[DCL07-A. Include the appropriate type information in function declarators]].

Compliant Solution: (function pointers)

Properly declaring fp so it is compatible with strchr() corrects this example.

#include <string.h>

char *(*fp) (const char *,int);

int main(void) {
  char *c;
  fp = strchr;
  c = fp("Hello",'H');
  printf("%s\n",c);

}

Non-Compliant Code Example: (variadic functions)

The POSIX function open() [[Open Group 04]] is a variadic function with the following prototype:

int open(const char *path, int oflag, ... );

The open() function accepts a third argument to determine a newly created file's access mode. If open() is used to create a new file and the third argument is omitted, the file may be created with unintended access permissions [[FIO06-A. Create files with appropriate access permissions]].

/* ... */
int fd = open(file_name, O_CREAT | O_WRONLY); /* access permissions are missing */
if (fd == -1){
  /* Handle Error */
}
/* ... */

Compliant Solution: (variadic functions)

To correct this example, a third argument is specified in the call to open().

/* ... */
int fd = open(file_name, O_CREAT | O_WRONLY, file_access_permissions);
if (fd == -1){
  /* Handle Error */
}
/* ... */