Library Functions Questions and Answers

Q: Which of the following library functions is used to read location dependent information?

Correct answer: localeconv()localeconv() returns a pointer to a struct lconv describing the current locale’s numeric and monetary conventions - the decimal point, the thousands separator, the currency symbol and where it goes. localtime() converts a time and has nothing to do with locales in this sense.

Q: Determine Output: #include <stdio.h> #define a 10 void main() { #define a 50 printf("%d", a); }

Correct answer: 50The preprocessor works on the text in order and takes no notice of braces, so the second #define is in force by the time the printf line is expanded - and the program prints 50. Redefining a macro to a different value without an intervening #undef is not strictly conforming, so expect a warning.

Q: The header file assert.h of the C Standard Library defines ________macro.

Correct answer: assert<assert.h> defines exactly one thing: the assert macro, which tests a condition and, if it is false, prints the expression, the file and the line and calls abort(). Defining NDEBUG before the include turns every assertion into nothing, which is how they are removed from a release build.

Q: Data written into a file using fwrite() can be read back using fscanf()

Correct answer: Falsefwrite writes data in its binary representation, while fscanf reads formatted text. The two do not match: an int written by fwrite is four raw bytes, not the digits %d expects. Data written with fwrite must be read back with fread.

Q: The itoa function can convert an integer in decimal, octal or hexadecimal form to a string.

Correct answer: Yesitoa(value, buffer, base) takes a base as its third argument, so it will produce the decimal, octal, hexadecimal or binary representation. It is not a standard C function - it belongs to the Turbo C and Microsoft libraries - and sprintf is the portable substitute.

Q: The function strlen() includes the terminating null character in the length it returns.

Correct answer: Falsestrlen() counts only the characters before the terminating null, so strlen("abc") is 3. The array holding that string nevertheless needs 4 bytes, which is why sizeof and strlen give different answers.

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: If the two strings are found to be unequal then strcmp returns difference between the first non-matching pair of characters.

Correct answer: Truestrcmp compares character by character and, at the first difference, returns the difference between those two characters - negative, zero or positive. Only the sign is guaranteed by the standard, so code should test < 0 or > 0 rather than expect a particular number.

Q: The assert macro returns __________ value.

Correct answer: noassert is a void macro: it returns nothing. If the condition holds it does nothing at all; if it fails it prints the expression, the file and the line and calls abort(). So it can never appear where a value is wanted.

31.

Which of the following library functions is used to read location dependent information?

A.localtime()
B.localeconv()
C.localcon()
D.local()

Answer: B

Correct answer: localeconv()

localeconv() returns a pointer to a struct lconv describing the current locale’s numeric and monetary conventions - the decimal point, the thousands separator, the currency symbol and where it goes. localtime() converts a time and has nothing to do with locales in this sense.

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32.

Determine Output:

#include <stdio.h>
#define a 10
void main()
{
      #define a 50
      printf("%d", a);
}

A.50
B.10
C.Compiler Error
D.None of These

Answer: A

Correct answer: 50

The preprocessor works on the text in order and takes no notice of braces, so the second #define is in force by the time the printf line is expanded - and the program prints 50. Redefining a macro to a different value without an intervening #undef is not strictly conforming, so expect a warning.

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33.

The header file assert.h of the C Standard Library defines ________macro.

A.stderr
B.stdarg
C.setjmp
D.assert

Answer: D

Correct answer: assert

<assert.h> defines exactly one thing: the assert macro, which tests a condition and, if it is false, prints the expression, the file and the line and calls abort(). Defining NDEBUG before the include turns every assertion into nothing, which is how they are removed from a release build.

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34.

Data written into a file using fwrite() can be read back using fscanf()

A.True
B.False

Answer: B

Correct answer: False

fwrite writes data in its binary representation, while fscanf reads formatted text. The two do not match: an int written by fwrite is four raw bytes, not the digits %d expects. Data written with fwrite must be read back with fread.

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35.

The itoa function can convert an integer in decimal, octal or hexadecimal form to a string.

A.Yes
B.No

Answer: A

Correct answer: Yes

itoa(value, buffer, base) takes a base as its third argument, so it will produce the decimal, octal, hexadecimal or binary representation. It is not a standard C function - it belongs to the Turbo C and Microsoft libraries - and sprintf is the portable substitute.

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36.

The function strlen() includes the terminating null character in the length it returns.

A.True
B.False

Answer: B

Correct answer: False

strlen() counts only the characters before the terminating null, so strlen("abc") is 3. The array holding that string nevertheless needs 4 bytes, which is why sizeof and strlen give different answers.

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37.

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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38.

Will the program outputs "IndiaBIX.com"?

#include <stdio.h>
#include <string.h>

int main()
{
    char str1[] = "IndiaBIX.com";
    char str2[20];
    strncpy(str2, str1, 8);
    printf("%s", str2);
    return 0;
}

A.Yes
B.No

Answer: B

No. It will print something like 'IndiaBIX(some garbage values here)' .

Because after copying the first 8 characters of source string into target string strncpy() doesn't terminate the target string with a '\0'. So it may print some garbage values along with IndiaBIX.

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39.

If the two strings are found to be unequal then strcmp returns difference between the first non-matching pair of characters.

A.True
B.False

Answer: A

Correct answer: True

strcmp compares character by character and, at the first difference, returns the difference between those two characters - negative, zero or positive. Only the sign is guaranteed by the standard, so code should test < 0 or > 0 rather than expect a particular number.

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40.

The assert macro returns __________ value.

A.integer
B.float
C.double
D.no

Answer: D

Correct answer: no

assert is a void macro: it returns nothing. If the condition holds it does nothing at all; if it fails it prints the expression, the file and the line and calls abort(). So it can never appear where a value is wanted.

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