Question

I want to emit dynamic error messages like all interpreters do nowadays, for example:

Name error: Undefined variable

would be constant, however what I want to reach is:

Name error: Undefined variable 'X', in line 1

Okay. The line number was really no problem: Every error message must have a line number, so I added it to the error emitter function:

Error( ErrType type, string msg, int line );

So where is my problem?

How do I get the 'X' into Undefined variable *?

• I can’t use sprintf as it doesn’t support strings yet I use them everywhere
• I can’t simply use cout and connect everything as I want error messages to be supressable
• I’d like to get everything into one function like above, Error()

How do I put together dynamic error messages?

For example: Error( Name, sprintf("Undefined variable %s", myVariableName ), lineNum );

(But myVariableName is a string and sprintf will mess things up)

Answer 1

You can get a null-terminated C string out of myVariableName by calling c_str:

myVariableName.c_str()

Note that your use of sprintf is incorrect; the first parameter of sprintf takes the buffer into which to place the formatted string. If you are using std::string in your program, why use sprintf at all? If Error takes a std::string then you can just use string concatenation:

Error(Name, "Undefined variable " + myVariableName, lineNum);