Padding specified number of zeros to a char array

Question

I want to pad a given char array to make it a 15 character array.

For eg. if the array contains two characters 1, 2 then 13 0 characters should be padded to make in 000000000000012 and if contains five characters then 10 0s should be padded. The resultant array should contain 15 characters always.

Found one solution here but that’s for stl string I need similar solution for char arrays. Please help. What I have tried is below:

char moneyArray[256];
memset(moneyArray, 0, 256);    
for(int i=0;i<(15-strlen(moneyArray))-1;i++)
    sprintf(moneyArray,"0%s",moneyArray);

But I am looking for a standard solution if possible using a std function may be?

Answer 1

You can use the pad function below:

#include <iostream>
#include <cstring>

void pad(char *s, int n, int c) {
    char *p = s + n - strlen(s);
    strcpy(p, s);
    p--;
    while (p >= s) { p[0] = c; p--; }
}

int main () { 
    char b[16] = "123";
    pad(b, 15, '0');
    std::cout << b << std::endl;
    return 0; 
}

Answer 2

If you're fine with std::string (and I think you should be), you can make use of its fill constructor:

char        s[]    = "12";
std::string padded = std::string( (15 - strlen(s) ), '0').append(s);

Of course you might want to check whether strlen(s) > 15 first.