VC++ variables inside strings

[T0MMY]

Hi I'm just slowly getting to grips with C++ after years of clinging to VB. I seen a bit of code yesterday which looked something like:

cout << "Total Cost is %i% pounds", Total_Cost;

Where %i% inside the string is replace with the integer Total_Cost. As it turns out thats exactly what I need! I'm using a large string with many veriables inside, it's going to be a nightmare to manually split it all up. If I've typed the above code correctly, and people reconise it can you point me to where I can learn more?

Cheers

[MountainDew7]

lol I just saw this on Yahoo answers.

To seperate variables from "literal stuff" you use <<'s

string name,language;
name = "MountainDew";
language = "C++";
cout << "Hi I'm " << name << " and I'm coding in " << language << ".";
//HI I'm MountainDew and I'm coding in C++.

[penagate]

It should be noted that the << operator (with respect to std::cout) does not mean exactly "separate variables from literal stuff" but rather to write the right-hand side to the left-hand side (being stdout in this case).

In a more general sense, the joining of strings is called concatenation, and std::string (like the string classes in various other languages) defines the + operator for this purpose:

std::cout << "Hi, my name is " + name + " and I'm using " + language + "." << std::endl;

Note that this cannot be applied to two operands which are string literals, because the string literal represents a char array and not a std::string object:

  $ cat test2.cpp
#include <string>

int main()
{
  std::string test = "Hello " + "World";
  return 0;
}

  $ g++ test2.cpp -o test2
test2.cpp: In function ‘int main()’:
test2.cpp:5: error: invalid operands of types ‘const char [7]’ and ‘const char [6]’ to binary ‘operator+’

In this respect, the << operator is nice because it accepts anything that has a string representation.

[wossname]

I seen a bit of code yesterday which looked something like:
cout << "Total Cost is %i% pounds", Total_Cost;

I've not come across that coding style in C++ before but it looks very reminiscent of the way the printf() function works. Here's the equivalent printf() call...

printf("Total Cost is %d pounds\n", Total_Cost);

So I'd advise you to use printf() instead if you are hell-bent on this placeholder method of string catting.

In C++, I only ever use printf for quick and dirty debugging statements because the syntax is simpler and also you can rapidly find all your debugging-only statements later on by searching for " printf(" globally. Otherwise I use the awkward << syntax for outputting strings because it handles class types so well. There's nothing wrong with using printf() really but many people tend to frown upon it's use in C++ through a belief that it is somehow evil.