Could not get the entered string from the stack of function

Question

#include <stdio.h>

#include <stdlib.h>

static void get_string(char *ac)
{
    ac = (char *)malloc (1 * sizeof (char));
    printf("Enter the string to count vowels and consonants in a string using pointers: ");
    scanf("%s", ac);
}

main(int argc, char *argv[])
{
    char *ac = NULL;
    get_string(ac);
    printf("The Entered string is:%s", ac);
    for(;;);
}

Could not get the entered string from the stack of function. Returns null.Can anyone help me in debug?

If you allocate space for only **1** character, what string do you expect to get exactly? — StoryTeller - Unslander Monica, Sep 14 '17 at 07:36

score 1 · Answer 1 · answered Sep 14 '17 at 07:36

1

Function arguments in C is passed by value. Any changes made to the parameters from inside the called function will not reflect to the actual argument supplied at function call.

In your case, you wanted to change ac itself (not the content of the memory location it points to), so, that would need a pointer-to-ac.

That said,

Please see this discussion on why not to cast the return value of malloc() and family in C..
sizeof(char) is guaranteed to be 1 in C, no need to use it as multiplier
a memory allocation of 1 byte can only hold an empty string, that's probably meaningless (and erroneous) in your code.

answered Sep 14 '17 at 07:36

Sourav Ghosh

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Then what are the modification I need to do in the code? – jiju Sep 14 '17 at 07:51
Mallocate a sane length for your input, (256, say), use a width of [length-1] in your scanf() format string, and then either return the string from get_string() as a char* or use a double-pointer argument/parameter to allow the allocated pointer to be communicated back to the caller. Easiest to just return it. – Martin James Sep 14 '17 at 08:21
Oh - and free() the char* after printffing it in main(). – Martin James Sep 14 '17 at 08:22
..or change your design so that main() allocates the string space and 'get_string()' loads it up. Should probably pass in the string pointer and a max length in that case. – Martin James Sep 14 '17 at 08:25
@MartinJames I'd second the last idea, cleanest, IMHO. – Sourav Ghosh Sep 14 '17 at 08:51
I dont want to return anything to main.I wanted to change in the stack of main memory itself – jiju Sep 14 '17 at 09:16
https://ideone.com/uEQpqA – jiju Sep 14 '17 at 09:21
Hope this will work!! – jiju Sep 14 '17 at 09:21
@jiju [___DO NOT___ use `gets()`, it is dangerous. use `fgets()` instead.](https://stackoverflow.com/a/41383540/2173917) – Sourav Ghosh Sep 14 '17 at 09:32
@Sourav Ghosh Thanks sourav!!Can I know why? – jiju Sep 14 '17 at 09:46
@jiju That's there in the link... – Sourav Ghosh Sep 14 '17 at 09:46

Could not get the entered string from the stack of function

1 Answers1