GATE CSE 1997 | Question: 1.9

Question

The conditional expansion facility of macro processor is provided to

• A. test a condition during the execution of the expanded program
• B. to expand certain model statements depending upon the value of a condition during the execution of the expanded program
• C. to implement recursion
• D. to expand certain model statements depending upon the value of a condition during the process of macro expansion

Comments

Is macro in the sylllabus?

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@kathan Mistry As per 2023, No.

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@Shaik Masthan sir , @Deepak Poonia sir please explain option B.

Thanks

Answer 1

Macro is expanded during the process of macro expansion. Hence, correct answer would be (d).

Comments

Conditional Compilation

There are a whole set of options that can be used to determine whether the preprocessor will remove lines of code before handing the file to the compiler. They include #if, #elif, #else, #ifdef, and #ifndef. An #if or #if/#elif/#else block or a #ifdef or #ifndef block must be terminated with a closing #endif.

The #if directive takes a numerical argument that evaluates to true if it's non-zero. If its argument is false, then code until the closing #else, #elif, of #endif will be excluded.

https://www.cprogramming.com/tutorial/cpreprocessor.html

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Hello Aspi, I am showing how conditional macro is expanded with an example. Consider the following C program.

#include <stdio.h>

#if (X<3)
#define Y 3
#else
#define Y 300
#endif
int main()
{
    printf("Value of Y is %d\n", Y);
    return 0;
}

 

Now save the above program as example.c and compile in the following ways.

gcc -E -DX=1 example.c

gcc -E -DX=10 example.c

Observe the outputs of both compilations (printf statement), you will understand how conditional macros are expanded during preprocessing phase.

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@suraj Could you give more insight on gcc -E -DX with few examples?

Answer 2

The conditional expansion facility of a macro processor is provided to expand certain model statements depending upon the value of a condition during the process of macro expansion.

This facility allows the macro processor to make decisions based on conditions and selectively include or exclude certain parts of the macro definition during the expansion process. It provides a way to customize the behavior of the macro expansion based on conditions specified in the source code or through parameters passed to the macro. This feature enhances the flexibility and adaptability of the macro processing mechanism.