C++ Token and Constant Concatenation

Question

My app requires me to change logos and icons every time it is compiled for each customer. Doing this by hand is, naturally, time consuming and error prone, so I have written the .Net form to load its images and icons from a .rc file, but I'm trying to work some preprocessor magic in the resources file.

My goal is to have it automatically load only one image and icon from a directory that has the customer's id. This will prevent the .rc file from linking unneeded images and files, and make setup for each customer as simple as a single prepcessor command.

I have a token called "CUSTOMER_ID" that is the folder name of their resources. So, their files would be in "../files/images/customer1/" where CUSTOMER_ID = customer1.

I want to get the preprocessor to concatenate the constant of "..files/images/" with CUSTOMER_ID, followed by "icon.ico" or "logo.bmp" so that I can define the resource. This is what I have currently:

//in resources.rc
#include "airline.h"
#define CONCAT(dir, cid, filetype) dir ## cid ## filetype

IDI_ICON1 ICON  CONCAT("../files/images/",CUSTOMER_ID,"icon.ico")

However, the results always end up off. Advice?

Answer 1

For RC files preprocessor directives are very limited, see: http://msdn.microsoft.com/en-us/library/windows/desktop/aa381033(v=vs.85).aspx

Directive   Description
#define         Defines a specified name by assigning it a given value.
#elif           Marks an optional clause of a conditional-compilation block.
#else           Marks the last optional clause of a conditional-compilation block.
#endif          Marks the end of a conditional-compilation block.
#if         Conditionally compiles the script if a specified expression is true.
#ifdef          Conditionally compiles the script if a specified name is defined.
#ifndef         Conditionally compiles the script if a specified name is not defined.
#include    Copies the contents of a file into the resource-definition file.
#undef          Removes the definition of the specified name.

And #define is of simple form: (after http://msdn.microsoft.com/en-us/library/windows/desktop/aa381061(v=vs.85).aspx):

#define name value

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There is solution - according to this answer prepare your ICON/BITMAPS paths as environment variables, you can build them from costumer name - but it must be done in your batchFile or makefile:

From the already mentioned answer:

In your project properties add ;$(CMDLINE_DEFINES) to the end of your resource preprocessor definitions. (Be sure to pick the right configuration.)

Then when you use MSBuild from the command line type (or add to a batch file)...

C:\Projects\SomeProject> set CMDLINE_DEFINES=SOMETEST=42
C:\Projects\SomeProject> MSBuild SomeProject.vcproj

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This answer was for C++ files:

For your example:

CONCAT("../files/images/",CUSTOMER_ID,"icon.ico")

You should use such macro:

#define TOSTRING(T) #T
#define CONCAT(dir, cid, filetype) dir TOSTRING(cid) filetype

This is because this macro expansion is: "../files/images/" "customer1" "icon.ico". And the C++ compiler will concatenate adjacent string literals.

This example:

#include <iostream>

#define TOSTRING(T) #T
#define CONCAT(dir, cid, filetype) dir TOSTRING(cid) filetype

#define CUSTOMER_ID customer1

int main() {
    std::cout << ">>>>>" << CONCAT("../files/images/",CUSTOMER_ID,"icon.ico") << "<<<<\n";
}

will produce output:

>>>>>../files/images/customer1icon.ico<<<<

Possible you should add / before icon.ico...