How to append a char to a std::string?

Question

The following fails with the error prog.cpp:5:13: error: invalid conversion from ‘char’ to ‘const char*’

int main()
{
  char d = \'d\';
  std::s         


        

Answer 1

In addition to the others mentioned, one of the string constructors take a char and the number of repetitions for that char. So you can use that to append a single char.

std::string s = "hell";
s += std::string(1, 'o');

Answer 2

y += d;

I would use += operator instead of named functions.

Answer 3

To add a char to a std::string var using the append method, you need to use this overload:

std::string::append(size_type _Count, char _Ch)

Edit : Your're right I misunderstood the size_type parameter, displayed in the context help. This is the number of chars to add. So the correct call is

s.append(1, d);

not

s.append(sizeof(char), d);

Or the simpliest way :

s += d;

Answer 4

Try the += operator link text, append() method link text, or push_back() method link text

The links in this post also contain examples of how to use the respective APIs.

Answer 5

If you are using the push_back there is no call for the string constructor. Otherwise it will create a string object via casting, then it will add the character in this string to the other string. Too much trouble for a tiny character ;)

Answer 6

I test the several propositions by running them into a large loop. I used microsoft visual studio 2015 as compiler and my processor is an i7, 8Hz, 2GHz.

    long start = clock();
    int a = 0;
    //100000000
    std::string ret;
    for (int i = 0; i < 60000000; i++)
    {
        ret.append(1, ' ');
        //ret += ' ';
        //ret.push_back(' ');
        //ret.insert(ret.end(), 1, ' ');
        //ret.resize(ret.size() + 1, ' ');
    }
    long stop = clock();
    long test = stop - start;
    return 0;

According to this test, results are :

     operation             time(ms)            note
------------------------------------------------------------------------
append                     66015
+=                         67328      1.02 time slower than 'append'
resize                     83867      1.27 time slower than 'append'
push_back & insert         90000      more than 1.36 time slower than 'append'

Conclusion

+= seems more understandable, but if you mind about speed, use append