w3resource

C free() function

C free() function - Free allocated memory

Syntax:

void free(void *ptr)

The free() function is used to free a block of storage. The ptr argument points to a block that is previously reserved with a call to the calloc(), malloc(), realloc().

Parameters:

Name Description Required /Optional
ptr Previously allocated memory block to be freed. Required

Return value from free()

  • There is no return value.

Example: free() function

The following example shows the usage of free() function.


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

int main () {
   char *str;

   /* Initial memory allocation */
   str = (char *) malloc(10);
   strcpy(str, "w3resource");
   printf("String = %s,  Address = %u\n", str, str);

   /* Deallocate allocated memory */
   free(str);
   return(0);
}

Output:

String = w3resource,  Address = 7738336

C Programming Code Editor:

Previous C Programming: C calloc()
Next C Programming: C malloc()



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C Programming: Tips of the Day

Returning an array using C

You can't return arrays from functions in C. You also can't (shouldn't) do this:

char *returnArray(char array []){
 char returned [10];
 //methods to pull values from array, interpret them, and then create new array
 return &(returned[0]); //is this correct?
}

returned is created with automatic storage duration and references to it will become invalid once it leaves its declaring scope, i.e., when the function returns.

You will need to dynamically allocate the memory inside of the function or fill a preallocated buffer provided by the caller.

Dynamically allocate the memory inside of the function (caller responsible for deallocating ret)

char *foo(int count) {
    char *ret = malloc(count);
    if(!ret)
        return NULL;

    for(int i = 0; i < count; ++i) 
        ret[i] = i;

    return ret;
}

Call it like so:

int main() {
    char *p = foo(10);
    if(p) {
        // do stuff with p
        free(p);
    }

    return 0;
}

Ref : https://bit.ly/3yFIeao

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