This page covers how to use the define in a macro form in C to get better control over the debugging output using a verbosity variable, here called show1.

Almost all production code has some form of diagnostic debugging output controlled by some verbosity switch.

At the operating system level, Windows, Linux, Android, etc, for example, create events that are saved for diagnostic use with ways to filter events to see what is happening.

The program inputs an integer variable (without prompt) that determines whether diagnostic output is shown according to the following values.

• If 0, no extra output is shown, just the final results (no condition necessary)
• If 1, output from processing and the final result, are shown (condition "greater than zero").
• If 2, all output, including prompts and echo, is shown (condition "greater than one").

Here is the code to use debugging variables as has been done to this point.

The program reads in the debugging output variable value.

Then it reads two integers, computes the sum, and outputs that sum. Here is the C code [#1]
#include <stdio.h> int main() { int show1; int x1; int y1; int z1; // input scanf("%d",&show1); if (show1 > 1) { printf("Input two integers.\n"); } scanf("%d %d",&x1,&y1); if (show1 > 1) { printf("You entered %d and %d.\n",x1,y1); } // process z1 = x1 + y1; if (show1 > 0) { printf("Process: %d and %d to get %d\t", x1, y1, z1); } // output printf("Output: %d + %d is %d\n",x1,y1,z1); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
2 2 3
For the above example input, here is the expected output.
Input two integers. You entered 2 and 3. Process: 2 and 3 to get 5 Output: 2 + 3 is 5
Here is an example input.
1 5 7
For the above example input, here is the expected output.
Process: 5 and 7 to get 12 Output: 5 + 7 is 12
Here is an example input.
0 11 13
For the above example input, here is the expected output.
Output: 11 + 13 is 24

To make the code more concise and readable, the following macros are introduced.
#define printf0(...) printf(__VA_ARGS__) #define printf1(...) if (show1 > 0) printf(__VA_ARGS__) #define printf2(...) if (show1 > 1) printf(__VA_ARGS__)
Note that it is not good style in a program to use single-line if statements with one statement. But here, the macro is doing the work and we never see that single-line if statement.

The macro definition feature works with a call by text method. The three dots "..." are used to indicate consider all arguments provided as text for replacement.

The __VA_ARGS__ variable includes all the text provided as an argument to the macro.

Now how cleaner the code looks and how easy it is to change.

To automatically remove all debugging output code from the executable program, one can use the following defines.
#define printf0(...) printf(__VA_ARGS__) #define printf1(...) #define printf2(...)
Note: These defines can also be controlled at a meta level and from arguments provided from the command line.

Note that these debugging macro definitions could be put in a separate header file and then included so that the same definitions can be shared across many code files.

Note: If the compiler complains about a missing code file, one can create an empty one with a comment and, if necessary, one function or variable. Here is the C code [#4]
#include <stdio.h> #define printf0(...) printf(__VA_ARGS__) #define printf1(...) if (show1 > 0) printf(__VA_ARGS__) #define printf2(...) if (show1 > 1) printf(__VA_ARGS__) int main() { int show1; int x1; int y1; int z1; // input scanf("%d",&show1); printf2("Input two integers.\n"); scanf("%d %d",&x1,&y1); printf2("You entered %d and %d.\n",x1,y1); // process z1 = x1 + y1; printf1("Process: %d and %d to get %d\t", x1, y1, z1); // output printf0("Output: %d + %d is %d\n",x1,y1,z1); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
2 2 3
For the above example input, here is the expected output.
Input two integers. You entered 2 and 3. Process: 2 and 3 to get 5 Output: 2 + 3 is 5
Here is an example input.
1 5 7
For the above example input, here is the expected output.
Process: 5 and 7 to get 12 Output: 5 + 7 is 12
Here is an example input.
0 11 13
For the above example input, here is the expected output.
Output: 11 + 13 is 24

The use of this macro is very human efficient in programming. This type of debugging code is not in a time-critical place. So the effect is as if one wrote a separate if statement for each such output statement. But the computer is doing this work and makes it easier for the programmer.

Finally, the program below toggles debug output on and off at the compile level using a preprocessor symbol SHOW1. Thus, all debug output in the generated/compiled code can be turned on or off in one place.

And, if necessary, the symbol SHOW1 can be set from the command line when the program is compiled. Notice now, if SHOW1 is not defined, it does not matter what the variable show1 contains, only production output is done.

Such symbols and a preprocessor, such is in C, C++, C#, etc., are often used in production code to include or not include certain code depending on the target platform, such is Windows, Linux, Apple, Android, etc. Here is the C code [#5]
#include <stdio.h> #define SHOW1 #undef SHOW1 #ifdef SHOW1 #define printf0(...) printf(__VA_ARGS__) #define printf1(...) if (show1 > 0) printf(__VA_ARGS__) #define printf2(...) if (show1 > 1) printf(__VA_ARGS__) #else #define printf0(...) printf(__VA_ARGS__) #define printf1(...) #define printf2(...) #endif int main() { int show1; int x1; int y1; int z1; // input scanf("%d",&show1); printf2("Input two integers.\n"); scanf("%d %d",&x1,&y1); printf2("You entered %d and %d.\n",x1,y1); // process z1 = x1 + y1; printf1("Process: %d and %d to get %d\n", x1, y1, z1); // output printf0("Output: %d + %d is %d\n",x1,y1,z1); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
2 2 3
For the above example input, here is the expected output.
Output: 2 + 3 is 5
Here is an example input.
1 5 7
For the above example input, here is the expected output.
Output: 5 + 7 is 12
Here is an example input.
0 11 13
For the above example input, here is the expected output.
Output: 11 + 13 is 24

The C (and C++) macro and directive preprocessor provide a powerful meta-programming way to control code generation in software projects at any level.