Typedef Questions and Answers

Q: Which of the following header files must necessarily be included to use dynamic memory allocation functions?

Correct answer: stdlib.hstdlib.h declares malloc, calloc, realloc and free, along with size_t.Including it matters more than it may appear. Without the prototype, an older compiler assumes malloc returns int, and on a machine where a pointer is wider than an int the returned address is truncated - a fault that a cast to the target type will silence rather than reveal. That is one of the strongest arguments against casting the result in C.

Q: What will be the output of the program? #include <stdio.h> int main() { typedef float f; static f *fptr; float fval = 90; fptr = &fval; printf("%f\n", *fptr); return 0; }

Correct answer: 90.000000f is an alias for float, so f *fptr is a float *. It is assigned the address of fval, and *fptr retrieves 90. Passed to printf, a float is promoted to double and %f prints it with six decimal places, giving 90.000000 rather than 90. The static qualifier affects storage duration only.

Q: typedef's have the advantage that they obey scope rules, that is they can be declared local to a function or a block whereas #define's always have a global effect.

Correct answer: YesThe statement is correct, and it follows from where each is processed. A typedef is a declaration handled by the compiler, so it obeys the ordinary scope rules and one declared inside a function or block is invisible outside it. A #define is handled by the preprocessor, which knows nothing of blocks, so it applies from its definition to the end of the file or until #undef.

61.

Which of the following header files must necessarily be included to use dynamic memory allocation functions?

A.stdlib.h
B.stdio.h
C.memory.h
D.dos.h

Answer: A

Correct answer: stdlib.h

stdlib.h declares malloc, calloc, realloc and free, along with size_t.

Including it matters more than it may appear. Without the prototype, an older compiler assumes malloc returns int, and on a machine where a pointer is wider than an int the returned address is truncated - a fault that a cast to the target type will silence rather than reveal. That is one of the strongest arguments against casting the result in C.

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62.

What will be the output of the program?

#include <stdio.h>

int main()
{
    typedef float f;
    static f *fptr;
    float fval = 90;
    fptr = &fval;
    printf("%f\n", *fptr);
    return 0;
}

A.9
B.90.000000
C.90

Answer: B

Correct answer: 90.000000

f is an alias for float, so f *fptr is a float *. It is assigned the address of fval, and *fptr retrieves 90. Passed to printf, a float is promoted to double and %f prints it with six decimal places, giving 90.000000 rather than 90. The static qualifier affects storage duration only.

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63.

typedef's have the advantage that they obey scope rules, that is they can be declared local to a function or a block whereas #define's always have a global effect.

A.Yes
B.No

Answer: A

Correct answer: Yes

The statement is correct, and it follows from where each is processed. A typedef is a declaration handled by the compiler, so it obeys the ordinary scope rules and one declared inside a function or block is invisible outside it. A #define is handled by the preprocessor, which knows nothing of blocks, so it applies from its definition to the end of the file or until #undef.

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