Compatible functions (C only)

For two function types to be compatible, they must meet the following requirements:

• They must agree in the number of parameters (and use of ellipsis).
• They must have compatible return types.
• The corresponding parameters must be compatible with the type that results from the application of the default argument promotions.

The composite type of two compatible function types is determined as follows:

• If one of the function types has a parameter type list, the composite type is a function prototype with the same parameter type list.
• If both function types have parameter type lists, the composite type of each parameter is determined as follows:
  • The composite of parameters of different rank is the type that results from the application of the default argument promotions.
  • The composite of parameters with array or function type is the adjusted type.
  • The composite of parameters with qualified type is the unqualified version of the declared type.

For example, for the following two function declarations:

int f(int (*)(), double (*)[3]); 
int f(int (*)(char *), double (*)[]);

The resulting composite type would be:

int f(int (*)(char *), double (*)[3]);

If the function declarator is not part of the function declaration, the parameters may have incomplete type. The parameters may also specify variable length array types by using the [*] notation in their sequences of declarator specifiers. The following are examples of compatible function prototype declarators:

int myMin(int n, int m, int a[n][m]);
int myMin(int n, int m, int a[*][*]);
int myMin(int n, int m, int a[ ][*]);
int myMin(int n, int m, int a[ ][m]);