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

I was looking the topic because Im developing VCL; Anyway making a function wasn't not so hard.

void addWhiteSpcs(string &str, int maxLength) {
    int i, length;

    length = str.length();
    for(i=length; i<maxLength; i++)
    str += " ";
};

string name1 = "johnny";
string name2 = "cash";

addWhiteSpcs(name1, 10);
addWhiteSpcs(name2, 10);

In both cases it will add to the right 10 blank spaces. I Recomend to use monospace fonts like courier or consolas for a correct format.

This is what happens when you're not using monospace font
johnny____
cash______

// using monospace font the output will be
johnny____
cash______

Both cases have the same length.

Answer 2

you can create a string containing N spaces by calling

string(N, ' ');

So you could do like this:

string to_be_padded = ...;
if (to_be_padded.size() < 10) {
  string padded(10 - to_be_padded.size(), ' ');
  padded += to_be_padded;
  return padded;
} else { return to_be_padded; }

Answer 3

std::string pad_right(std::string const& str, size_t s)
{
    if ( str.size() < s )
        return str + std::string(s-str.size(), ' ');
    else
        return str;
}

std::string pad_left(std::string const& str, size_t s)
{
    if ( str.size() < s )
        return std::string(s-str.size(), ' ') + str;
    else
        return str;
}

Answer 4

std::setw (setwidth) manipulator

std::cout << std::setw (10) << 77 << std::endl;

or

std::cout << std::setw (10) << "hi!" << std::endl;

outputs padded 77 and "hi!".

if you need result as string use instance of std::stringstream instead std::cout object.

ps: responsible header file <iomanip>

Answer 5

string t = string(10, ' ') + to_string(123);
cout << t.substr(t.size() - 10) << endl;

Try it online!

Answer 6

Create a new string of 10 spaces, and work backwards in both string.

string padstring(const string &source, size_t totalLength, char padChar)
{
    if (source.length() >= totalLength) 
        return source;

    string padded(totalLength, padChar);
    string::const_reverse_iterator iSource = source.rbegin();
    string::reverse_iterator iPadded = padded.rbegin();
    for (;iSource != source.rend(); ++iSource, ++iPadded)
        *iPadded = *iSource;
    return padded;
}