std::string formatting like sprintf

Question

I have to format std::string with sprintf and send it into file stream. How can I do this?

Answer 1

I wrote my own using vsnprintf so it returns string instead of having to create my own buffer.

#include 
#include 

//missing string printf
//this is safe and convenient but not exactly efficient
inline std::string format(const char* fmt, ...){
    int size = 512;
    char* buffer = 0;
    buffer = new char[size];
    va_list vl;
    va_start(vl, fmt);
    int nsize = vsnprintf(buffer, size, fmt, vl);
    if(size<=nsize){ //fail delete buffer and try again
        delete[] buffer;
        buffer = 0;
        buffer = new char[nsize+1]; //+1 for /0
        nsize = vsnprintf(buffer, size, fmt, vl);
    }
    std::string ret(buffer);
    va_end(vl);
    delete[] buffer;
    return ret;
}

So you can use it like

std::string mystr = format("%s %d %10.5f", "omg", 1, 10.5);