Thread: pointer to function

Hi everyone,

What is the difference between a pointer to a function that returns a pointer, to a function that takes a pointer as argument?

1) Passing a pointer to a function and returning it after operations

Code:

void iarray2d(int **mat, size_t nrows, size_t ncols, int index)
{
	//nrows = number of rows
	//ncols = ncolumns
	//index = 1 if you want allocation in the fortran way starting from 1
	//index = 0 if you want the standard C allocation way starting from 0
	
	long i;

	//Malloc pointers to rows
	mat= malloc((nrows+index)*sizeof(int*));
	if (!mat){
		printf("Matrix MAT could not be allocted");
		exit(1);
	}
	
	mat[0] = NULL;

	for(i=index; i<nrows+index; i++){
		mat[i] = malloc((ncols+index)*sizeof(int*));
		if (!mat[i]){
			printf("Matrix MAT could not be allocted\n The exec. will Exit now\n");
			exit(1);
		}
	}
	
return;
}

2) returning a pointer from a pointer to function

Code:

int **iarray2d(size_t nrows, size_t ncols, int index)
{
      	long i;
	int **mat;

	//Malloc pointers to rows
	mat= malloc((nrows+index+1)*sizeof(int*));
	if (!mat){
		printf("Matrix MAT could not be allocted");
		exit(1);
	}
	
	mat[0] = NULL;
	for(i=index; i<nrows+index; i++){
		mat[i] = malloc((ncols+index+1)*sizeof(int*));
		if (!mat[i]){
			printf("Matrix MAT could not be allocted\n The exec. will Exit now\n");
			exit(1);
		}
	}
	
return mat;
}

Thank you in advance
All the best

cfd

Originally Posted by matsp

Depends on how you intend to use it. Both are valid.

By the way, in a void function, you don't need a return.

--
Mats

Hi Mat, thanks for replying. I posted a reply also to the thread "dynamic allocation from 1 instead of zero" because I get a BUS error with the first option, where the function is not a pointer to function, but the argument is passed as a pointer.

Hi c.user,

thank you very much for your suggestion and for attaching your function. It'll be very helpful.

To answer your question on INDEX, it is because I not always want to allocate from zero, but also want to be able to allocate from 1; that's why I have the index variable as argument

all the best

ah... I'm understand, I would write second function which use normal function and call it with index added to nrows and ncols

Code:

int **CreateIndexMatrix(unsigned n, unsigned m, unsigned idx)
{
    return CreateMatrix(n+idx, m+idx);
}

it's a shell for base function

Hello there,
thank you for the hint

Best regards
cfd