Padding stl strings in C++

Question

I\'m using std::string and need to left pad them to a given width. What is the recommended way to do this in C++?

Sample input:

123


        

Answer 1

The easiest way I can think of would be with a stringstream:

string foo = "foo";
stringstream ss;
ss << setw(10) << foo;
foo = ss.str();

foo should now be padded.

Answer 2

There's a nice and simple way :)

const int required_pad = 10;

std::string myString = "123";
size_t length = myString.length();

if (length < required_pad)
  myString.insert(0, required_pad - length, ' ');

Answer 3

void padTo(std::string &str, const size_t num, const char paddingChar = ' ')
{
    if(num > str.size())
        str.insert(0, num - str.size(), paddingChar);
}

int main(int argc, char **argv)
{
    std::string str = "abcd";
    padTo(str, 10);
    return 0;
}

Answer 4

Minimal working code:

#include <iostream>
#include <iomanip>

int main()
{
    for(int i = 0; i < 300; i += 11)
    {
        std::cout << std::setfill ( ' ' ) << std::setw (2) << (i % 100) << std::endl;
    }
    return 0;
}

/*
Note:
- for std::setfill ( ' ' ):
  - item in '' is what will be used for filling
- std::cout may be replaced with a std::stringstream if you need it
- modulus is used to cut the integer to an appropriate length, for strings use substring
- std::setw is used to define the length of the needed string
*/

Answer 5

How about:

string s = "          "; // 10 spaces
string n = "123";
n.length() <= 10 ? s.replace(10 - n.length(), n.length(), s) : s = n;

Answer 6

You can use it like this:

std::string s = "123";
s.insert(s.begin(), paddedLength - s.size(), ' ');