Quick formatted strings in C++

Question

Is there a quick, easy way of getting sprintf-like formatting when constructing a std::string? Something like...

std::string foo("A number (%d) and a character (%c).\n", 18, 'a');

Answer 1

Not built into the string's constructor, but you might want to check out boost format. Its a more typesafe sprintf style string formatting. With it you can at least do this:

std::string foo = 
    boost::str(boost::format("A number (%d) and a character (%c)\n") % 18 % 'a');

Answer 2

I've written a stringbuilder class which you can use and I think that is better than boost::format as unlike it, stringbuilder does NOT use C-style format string like %d, %c. etc.

Here is how stringbuilder can help you in just one line:

std::string s=stringbuilder() << "A number " << 18 <<" and a character " <<'a';

The implementation of stringbuilder is very simple:

struct stringbuilder
{
   std::stringstream ss;
   template<typename T>
   stringbuilder & operator << (const T &data)
   {
        ss << data;
        return *this;
   }
   operator std::string() { return ss.str(); }
};

Demo at ideone : http://ideone.com/J9ALB

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I've just written the following blog describing the many different ways of the use of stringbuilder.

• Create string on the fly just in one line