Replacing characters in a string in C++

Question

In my application, I will be retrieving error message strings from a database. I would like to substitute numbers into the error message. The error message will be a C style string like:

Message %d does not exist

or

Error reading from bus %d

Ideally, I would like to be able to do a C style printf using this statement, and substituting my own numbers in. I know I can just do it manually, but is there an easier way to somehow use it like a string in a regular printf?

Answer 1

Apart for simple string concatenation or using << together with number and a message.

I can think of boost::format

int message_no=5;
std::cout << boost::format("Message %d doesn't exist") % message_no ;

Answer 2

The C++ way is to use std::stringstream:

std::stringstream str;
str << "Message " << messageName << " doesn't exist";

std::string out = str.str();

There is also very nice header-only boost string algorithms library :

std::string message = "Message %s doesn't exist";
boost::replace_first( str, "%s", "MyMessage" );

// message == "Message MyMessage doesn't exist"

and boost::format , which acts like printf, but is entirely type-safe and supports all user-defined types:

std::string out = format( "Message %1 doesn't exist" ) % "MyMessage";