Return Type
The return type of a function establishes the size and type of the value returned by the function. It corresponds to the type-specifier
in the Syntax section:
Syntax
function-definition
:
declaration-specifiers
opt attribute-seq
opt declarator
declaration-list
opt compound-statement
/* attribute-seq
is Microsoft-specific */
declaration-specifiers
:
storage-class-specifier
declaration-specifiers
opt
type-specifier
declaration-specifiers
opt
type-qualifier
declaration-specifiers
opt
type-specifier
:
void
char
short
int
__int8
/* Microsoft-specific */
__int16
/* Microsoft-specific */
__int32
/* Microsoft-specific */
__int64
/* Microsoft-specific */
long
long long
float
double
long double
signed
unsigned
struct-or-union-specifier
enum-specifier
typedef-name
The type-specifier
can specify any fundamental, structure, or union type.
The return type given in the function definition must match the return type in declarations of the function elsewhere in the program. A function returns a value when a return
statement containing an expression is executed. The expression is evaluated, converted to the return value type if necessary, and returned to the point at which the function was called. If a function is declared with return type void
, a return statement containing an expression generates a warning, and the expression isn't evaluated.
The following examples illustrate function return values.
typedef struct
{
char name[20];
int id;
long class;
} STUDENT;
/* Return type is STUDENT: */
STUDENT sortstu( STUDENT a, STUDENT b )
{
return ( (a.id < b.id) ? a : b );
}
This example defines the STUDENT
type with a typedef
declaration and defines the function sortstu
to have STUDENT
return type. The function selects and returns one of its two structure arguments. In subsequent calls to the function, the compiler checks to make sure the argument types are STUDENT
.
Note
Efficiency would be enhanced by passing pointers to the structure, rather than the entire structure.
char *smallstr( char s1[], char s2[] )
{
int i;
i = 0;
while ( s1[i] != '\0' && s2[i] != '\0' )
i++;
if ( s1[i] == '\0' )
return ( s1 );
else
return ( s2 );
}
This example defines a function returning a pointer to an array of characters. The function takes two character arrays (strings) as arguments and returns a pointer to the shorter of the two strings. A pointer to an array points to the first of the array elements and has its type; thus, the return type of the function is a pointer to type char
.
You need not declare functions with int
return type before you call them, although prototypes are recommended so that correct type checking for arguments and return values is enabled.