pointer and function argument question.

I am wondering if it is possible to have a function dynamically allocate some memory, as a character array, then return a pointer to that memory to the caller through one or more of the function arguments.

it may help to show the code I have been playing around with so I'll list it below.

Code:

---

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

int test_func(char *msg)
        {
        int i;
        char *bufptr;
        bufptr = (char *) calloc(100,sizeof(char));
        char recvd[] = "This is a test string";
        for(i=0;i<strlen(recvd);i++)
                {
                bufptr[i] = recvd[i];
                }
        msg = bufptr;
        printf("%s\n%s\n",msg,bufptr);
        return 0;
        }

int main()
        {
        char *msg;
        if(test_func(msg) == 0)
                {
                printf("%s\n",msg);
                }
        free(msg);
        }

---

The code compiles and runs on my Linux box, within tes_func the printf is able to successfully print msg and bufptr but in the main function when test_func is called and I try to print the string I had hoped would point to the dynamic string created within the function it segfaults.

Let me know if there is any way I can clarify this better.

btw I know the pointer can be returned using return, but I would like to be able to return multiple pointers to dynamically allocated strings with just one function and leave the return values such as -1 -2 -3 for telling the caller at what part of the function the problem occured.

Thanks

Steven Fletcher

Yes, it is possible. But remember that unless you pass a pointer to something, you cannot change its value in the caller (you must pass an int* to change the caller's int, for example). It thus follows that to modify a char*, you must pass a char**:

Code:

---

void f(char **msg)
{
  *msg = malloc(50);
}
int main(void)
{
  char *msg;
  f(&msg);
}

---

strlen() does not give you the length including the terminating zero, bufptr should be unterminated.

Thanks for the help. This makes much more sense now.

Luckily, It'll still work apart from pointer issue, because calloc() zeroed the memory.
It's better to use standard library function like strcpy/memcpy.

Are you referring to the for loop that copies the contents of recvd into bufptr? Or something else?