Higher-order functions

Pass a function as an argument.

C

Simple example, the pointer to the function to be passed as an argument is the only involved pointer.

Definition of a function whose only parameter is a pointer to a function with no parameters and no return value:

 void myFuncSimple( void (*funcParameter)(void) )
 {
      /* ... */
 
      *funcParameter();  /* Call the passed function. */
 
      /* ... */
 }

Call:

 void funcToBePassed(void);
 
 /* ... */
 
 myFuncSimple(&funcToBePassed);

Complex example.

Definition of a function whose return value is a pointer to int and whose only parameter is a pointer to a function, whose (in turn) return value is a pointer to double and whose only parameter is a pointer to long.

 int* myFuncComplex( double* (*funcParameter)(long* parameter) )
 {
      long* inLong;
      double* outDouble;
 
      /* ... */
 
      outDouble = *funcParameter(inLong);  /* Call the passed function and store returned pointer. */
 
      /* ... */
 }

Call:

 double* funcToBePassed(long* parameter);
 
 /* ... */
 
 int* outInt;  
 
 outInt = myFuncComplex(&funcToBePassed);

Finally, declaration of a pointer variable of the proper type to hold such a function as myFunc:

 int* (*funcPointer)( double* (*funcParameter)(long* parameter) );
 
 /* ... */
 
 funcPointer = myFuncComplex;

Of course, in a real project you shouldn't write such a convoluted code, but use some typedef instead, in order to break complexity into steps.

Perl

Interpreter: Perl

Passing a pointer to a function

my $retval = first('data', \&second);

sub first ($ $){
  my $val = shift;
  my $func = shift;
  return $func->($val);
}

sub second ($){
  return(reverse(shift));
}

Passing a string to be used as a function

my $retval = first('data', 'second');

sub first ($ $){
  my $val = shift;
  my $func = shift;
  return &{$func}($val);
}

sub second ($){
  return(reverse(shift));
}

C++

Same as C.