Predefined macros - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of __FILE__ and __LINE__ macros

What is the output of this C program when compiled and run?

C

#include <stdio.h>

int main() {
    printf("File: %s, Line: %d\n", __FILE__, __LINE__);
    return 0;
}

A File: main.c, Line: 7

B File: main.c, Line: 6

C File: main.c, Line: 4

D File: main.c, Line: 5

💡 Hint

Remember that __LINE__ expands to the line number where it appears in the source code.

The __FILE__ macro expands to the current file name as a string. The __LINE__ macro expands to the line number where it is used. The printf statement is on line 5 in the code snippet, so it prints Line: 5.

❓ Predict Output

intermediate

Output of __DATE__ and __TIME__ macros

What will this program print when compiled and run?

C

#include <stdio.h>

int main() {
    printf("Compiled on %s at %s\n", __DATE__, __TIME__);
    return 0;
}

A Compiled on Jun 15 2024 at 10:00:00 (example)

B Compiled on 2024-06-15 at 10:00:00

C Compiled on Jun 15 2024 at 10:00:00

D Compiled on Jun 15 2024 at 10:00:00 (actual compile time)

💡 Hint

The __DATE__ macro expands to a string literal in the format "Mmm dd yyyy".

The __DATE__ macro expands to the date when the source file was compiled, in the format "Mmm dd yyyy" (e.g., "Jun 15 2024"). The __TIME__ macro expands to the time of compilation in "hh:mm:ss" format. The output matches option C.

❓ Predict Output

advanced

Output of __STDC__ macro

What is the output of this program if compiled with a standard C compiler?

C

#include <stdio.h>

int main() {
#ifdef __STDC__
    printf("Standard C compiler detected\n");
#else
    printf("Non-standard compiler\n");
#endif
    return 0;
}

A Standard C compiler detected

B Non-standard compiler

C Compilation error due to undefined macro

D No output

💡 Hint

The __STDC__ macro is defined by standard C compilers.

The __STDC__ macro is predefined by standard C compilers to indicate compliance with the ANSI C standard. The #ifdef check succeeds, so the program prints "Standard C compiler detected".

❓ Predict Output

advanced

Output of __func__ macro inside a function

What does this program print when run?

C

#include <stdio.h>

void greet() {
    printf("Function name: %s\n", __func__);
}

int main() {
    greet();
    return 0;
}

A Function name: main

B Function name: greet

C Function name: __func__

D Function name: (null)

💡 Hint

The __func__ macro expands to the name of the current function as a string.

The __func__ macro expands to the name of the function where it is used. Since it is inside the greet() function, it prints "greet".

🧠 Conceptual

expert

Behavior of __LINE__ macro with macro expansion

Consider the following code. What is the output when compiled and run?

C

#include <stdio.h>

#define PRINT_LINE() printf("Line: %d\n", __LINE__)

int main() {
    PRINT_LINE();
    return 0;
}

A Line: 9

B Line: 5

C Line: 8

D Line: 7

💡 Hint

The __LINE__ macro expands to the line number where it appears after macro expansion.

The __LINE__ macro expands to the line number in the source code where it is used after macro expansion. Since PRINT_LINE() is called on line 9, __LINE__ expands to 9, so the output is "Line: 9".