How to write 'n' copies of a character to ostream like in python

Question

In python, the following instruction: print 'a'*5 would output aaaaa. How would one write something similar in C++ in conjunction with std::ostreams in order to avoid a for construct?

Answer 1

The obvious way would be with fill_n:

std::fill_n(std::ostream_iterator<char>(std::cout), 5, 'a');

Another possibility would be be to just construct a string:

std::cout << std::string(5, 'a');

Answer 2

Use some tricky way: os << setw(n) << setfill(c) << ""; Where n is number of char c to write

Answer 3

In C++20 you'll be able to use std::format to do this:

std::cout << std::format("{:a<5}", "");

Output:

aaaaa

In the meantime you can use the {fmt} library, std::format is based on. {fmt} also provides the print function that makes this even easier and more efficient (godbolt):

fmt::print("{:a<5}", "");

Disclaimer: I'm the author of {fmt} and C++20 std::format.

Answer 4

You can do something like that by overloading the * operator for std::string. Here is a small example

#include<iostream>
#include<string>
std::string operator*(const std::string &c,int n)
{
    std::string str;
    for(int i=0;i<n;i++)
    str+=c;
    return str;
}
int main()
{
    std::string str= "foo";
    std::cout<< str*5 <<"\n";
}

Answer 5

The standard does not provide any elegant way. But one possibility (my favourite) is to use a proxy object like this

class repeat_char
{
public:
    repeat_char(char c, size_t count) : c(c), count(count) {}
    friend std::ostream & operator<<(std::ostream & os, repeat_char repeat)
    {
        while (repeat.count-- > 0)
            os << repeat.c;
        return os;
    }
private:
    char c;
    size_t count;
};

and then use it this way

std::cout << repeat_char(' ', 5);