How do I concatenate multiple C++ strings on one line?

s += "Hello world, " + "nice to see you, " + "or not.";

Those character array literals are not C++ std::strings - you need to convert them:

s += string("Hello world, ") + string("nice to see you, ") + string("or not.");

To convert ints (or any other streamable type) you can use a boost lexical_cast or provide your own function:

template <typename T>
string Str( const T & t ) {
   ostringstream os;
   os << t;
   return os.str();
}

You can now say things like:

string s = string("The meaning is ") + Str( 42 );

Your code can be written as¹,

s = "Hello world," "nice to see you," "or not."

...but I doubt that's what you're looking for. In your case, you are probably looking for streams:

std::stringstream ss;
ss << "Hello world, " << 42 << "nice to see you.";
std::string s = ss.str();

¹ "can be written as" : This only works for string literals. The concatenation is done by the compiler.

In 5 years nobody has mentioned .append?

#include <string>

std::string s;
s.append("Hello world, ");
s.append("nice to see you, ");
s.append("or not.");

#include <sstream>
#include <string>

std::stringstream ss;
ss << "Hello, world, " << myInt << niceToSeeYouString;
std::string s = ss.str();

Take a look at this Guru Of The Week article from Herb Sutter: The String Formatters of Manor Farm

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