Returning a whole array in C-CodePudding

Hi I am pretty new to C and was wondering how to return an entire array. For example I have this function here.

char* foo(int x)
{
    char *num = (char*)malloc(x*sizeof(int));
    
    num[0] = '1';
    num[1] = '2';
    num[2] = '3';
    num[3] = '4';

    return num;
    
}

I realized that when I return num it only returns the first index of num. But is there any way to return the whole array, 1234? Any help will be greatly appreciated!

CodePudding user response：

Since the foo() function returns a pointer, you can see that all values are printed when you use the %s format specifier. The display() function prints the data in the memory area pointed to by the pointer as characters.

#include <stdio.h>
#include <stdlib.h>

char* foo(int x)
{
    char* num = (char*) malloc((x   1) * sizeof(char));
    
    for(size_t i = 0 ; i < x ;   i)
        num[i] = i   1   '0';
    num[x] = '\0';
    
    return num;
}

void display(char *array, size_t size)
{
    for(size_t i = 0 ; i < size && array[i] != '\0' ;   i)
        printf("array[%ld]: %c\n", i, array[i]);
}

int main()
{
    const size_t size = 4;
    char *result = foo(size); 
    
    printf("%s\n", result);
    display(result, size);
    
    return 0;
}

Output:

1234
array[0]: 1
array[1]: 2
array[2]: 3
array[3]: 4

CodePudding user response：

See if you are new to C, then learn it first do some googling and research. If you don't find anything then read some theory of a similar topic for examples (How to return an array in C?). After that some error is happening in your code then you can ask it on stackoverflow.

By the way your should be like:

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

char *foo(int x); // fix prototype errors
char *foo(int x)
{
    char *num = (char *)calloc(x   1, sizeof(char)); // we added  1 to append the null terminating character in `num`
    for (size_t i = 0; i < x; i  )
        num[i] = (char)(i   48);
    return num;
}

/* @returns no. of character written on stdout */
int print_foo(const char *num); // fix prototype errors
int print_foo(const char *num)
{
    if (num)
    {
        size_t z = 0;
        for (size_t i = 0; i < num[i] != '\0'; i  )
           z  =  fprintf(stdout, "num[%lu] = %c\n", i, num[i]);
        return z;
    }
    return -1;
}

int main(void)
{
    char *num = foo(10);
    print_foo((const char *)num);
    free(num); // free any heap allocated resources before exiting the application
    return 0;
}