Convert long long int to string without sprintf using functions

Question

I am trying to convert an unsigned long long int to a string without using any library functions like sprintf() or ltoi(). The problem is that when I return the value it doesn't return correctly, if I do not printf() in my function before returning it to the calling function.

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

char *myBuff;

char * loToString(unsigned long long int anInteger)
{  
    int flag = 0;
    char str[128] = { 0 }; // large enough for an int even on 64-bit
    int i = 126;

    while (anInteger != 0) { 
        str[i--] = (anInteger % 10) + '0';
        anInteger /= 10;
    }

    if (flag) str[i--] = '-';

    myBuff = str+i+1;
    return myBuff; 
}

int main() {
    // your code goes here

    unsigned long long int d;
    d=  17242913654266112;
    char * buff = loToString(d);

    printf("chu %s\n",buff);
    printf("chu %s\n",buff);


    return 0;

}

`char str[128] = { 0 };` It can not be used outside the scope. — BLUEPIXY, Mar 22 '17 at 04:27
In other words `mybuff` points to memory that was destroyed when `loToString` returned. (the function stack frame is destroyed/released back to the memory pool when the function returns). Allocate for `mybuff` before you pass to `loToString` or dynamically within `loToString`. — David C. Rankin, Mar 22 '17 at 04:36
"// large enough for an int even on 64-bit" - There is no maximum length of integer types. — too honest for this site, Mar 22 '17 at 06:59

jjm · Answer 1 · 2017-03-22T06:34:14.507

I modified few points

str should be allocated dynamically or should be in global scope. otherwise its scope will end after execution of loToString() and you are returning an address from str array.
char *myBuff is moved into local scope. Both is fine. But no need to declare it globally.

Check the modified code.

    char str[128]; // large enough for an int even on 64-bit, Moved to global scope 

    char * loToString(unsigned long long int anInteger)
    {  
        int flag = 0;
        int i = 126;
        char *myBuff = NULL;

        memset(str,0,sizeof(str));
        while (anInteger != 0) { 
            str[i--] = (anInteger % 10) + '0';
            anInteger /= 10;
        }

        if (flag) str[i--] = '-';

        myBuff = str+i+1;
        return myBuff; 
    }

Convert long long int to string without sprintf using functions

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