Library Functions Questions and Answers

Q: The pointer used in the mblen() function points to the _________

Correct answer: first byte of multibyte charactermblen(s, n) examines the multibyte character beginning at s - the pointer must therefore be at its first byte, since the length can only be determined from there. It returns how many bytes that character occupies, so that a program can step through a multibyte string.

Q: What will be the output of the following C code? int main () { printf("starting of program\n"); printf("program exits\n"); exit(0); printf("program ends\n"); return(0); }

Correct answer: starting of program program exitsexit(0) terminates the program immediately, so the third printf and the return are never reached. Only the first two lines appear. Unlike return from main, exit can be called from anywhere and ends the whole program.

Q: Some types and macros defined under the header file stddef.h may be defined under other header files too.

Correct answer: True<stddef.h> defines size_t, ptrdiff_t, wchar_t, NULL and offsetof - and several of these are also defined by other headers, so that a program including <stdio.h> gets size_t and NULL without asking. Repeating an identical definition is harmless.

Q: What will function gcvt() do?

Correct answer: Convert floating-point number to a stringgcvt() converts a floating-point number to a string, in the shorter of fixed and exponential notation for the requested number of significant digits. It is a non-standard function of the old Unix and Turbo C libraries; sprintf is the portable way to do the same thing.

Q: Which of the following is defined under the header file time.h?

Correct answer: NULLNULL is one of the few names defined in several headers at once, <time.h> among them - so a program gets it from whichever it happens to include. fabs belongs to <math.h>, iscntrl to <ctype.h> and the string functions to <string.h>.

Q: Which statement is true with respect to RAND_MAX?

Correct answer: specifies maximum value returned by rand()RAND_MAX is the largest value rand() can return, guaranteed to be at least 32767. It is needed to scale the result - rand() / (RAND_MAX + 1.0) gives a fraction between 0 and 1. srand returns nothing at all.

Q: Which type has an alignment requirement at least as large as that of every other data type?

Correct answer: max_align_tmax_align_t is an object type whose alignment requirement is at least as strict as that of every other scalar type. It matters to allocators: memory returned by malloc must be suitably aligned for any type, which is exactly this alignment. size_t and ptrdiff_t are integer types, and NULL is not a type at all.

101.

Is standard library a part of C language?

A.Yes
B.No

Answer: B

The C standard library consists of a set of sections of the ISO C standard which describe a collection of header files and library routines used to implement common operations, such as input/output and string handling, in the C programming language. The C standard library is an interface standard described by a document; it is not an actual library of software routines available for linkage to C programs.

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102.

What will the function rewind() do?

A.Reposition the file pointer to a character reverse
B.Reposition the file pointer stream to end of file
C.Reposition the file pointer to the beginning of that line
D.Reposition the file pointer to the beginning of the file

Answer: D

Correct answer: Reposition the file pointer to the beginning of the file

rewind(fp) moves the file position indicator back to the beginning of the file and clears the error and end-of-file flags. It is equivalent to fseek(fp, 0L, SEEK_SET), except that it returns nothing and resets the flags.

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103.

The pointer used in the mblen() function points to the _________

A.first byte of multibyte character
B.last byte of multibyte character
C.middle byte of multibyte character
D.no pointer is used in mblen function

Answer: A

Correct answer: first byte of multibyte character

mblen(s, n) examines the multibyte character beginning at s - the pointer must therefore be at its first byte, since the length can only be determined from there. It returns how many bytes that character occupies, so that a program can step through a multibyte string.

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104.

What will be the output of the following C code?

int main () 
{ 
   printf("starting of program\n"); 
   printf("program exits\n"); 
   exit(0);  
   printf("program ends\n");  
   return(0); 
}

A.starting of programprogram exitsprogram ends
B.starting of programprogram exits
C.starting of programprogram ends
D.error

Answer: B

Correct answer: starting of program program exits

exit(0) terminates the program immediately, so the third printf and the return are never reached. Only the first two lines appear. Unlike return from main, exit can be called from anywhere and ends the whole program.

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105.

Some types and macros defined under the header file stddef.h may be defined under other header files too.

A.True
B.False

Answer: A

Correct answer: True

<stddef.h> defines size_t, ptrdiff_t, wchar_t, NULL and offsetof - and several of these are also defined by other headers, so that a program including <stdio.h> gets size_t and NULL without asking. Repeating an identical definition is harmless.

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106.

What will function gcvt() do?

A.Convert vector to integer value
B.Convert floating-point number to a string
C.Convert a 2D array into a 1D array
D.Convert a multidimensional array into a 1D array

Answer: B

Correct answer: Convert floating-point number to a string

gcvt() converts a floating-point number to a string, in the shorter of fixed and exponential notation for the requested number of significant digits. It is a non-standard function of the old Unix and Turbo C libraries; sprintf is the portable way to do the same thing.

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107.

Which of the following is defined under the header file time.h?

A.strncat()
B.fabs()
C.iscntrl()
D.NULL

Answer: D

Correct answer: NULL

NULL is one of the few names defined in several headers at once, <time.h> among them - so a program gets it from whichever it happens to include. fabs belongs to <math.h>, iscntrl to <ctype.h> and the string functions to <string.h>.

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108.

Which statement is true with respect to RAND_MAX?

A.specifies value for status argument to exit indicating failure
B.specifies value for status argument to exit indicating success
C.specifies maximum value returned by rand()
D.specifies maximum value returned by srand()

Answer: C

Correct answer: specifies maximum value returned by rand()

RAND_MAX is the largest value rand() can return, guaranteed to be at least 32767. It is needed to scale the result - rand() / (RAND_MAX + 1.0) gives a fraction between 0 and 1. srand returns nothing at all.

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109.

Which type has an alignment requirement at least as large as that of every other data type?

A.max_align_t
B.ptrdiff_t
C.size_t
D.NULL

Answer: D

Correct answer: max_align_t

max_align_t is an object type whose alignment requirement is at least as strict as that of every other scalar type. It matters to allocators: memory returned by malloc must be suitably aligned for any type, which is exactly this alignment. size_t and ptrdiff_t are integer types, and NULL is not a type at all.

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110.

The purpose of the function ctime() is that ___________

A.it returns a string representing the local time
B.it returns a void string
C.it returns a string representing the time in UTC format
D.it returns a string representing the time stored in a structure

Answer: A

Correct answer: it returns a string representing the local time

ctime() takes a time_t and returns a printable string in local time, of the form Wed Jun 30 21:49:08 2021\n. It is asctime(localtime(t)) in one call. The string is in a static buffer, so it is overwritten by the next call.

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