Library Functions Questions and Answers

Q: FILE is a structure suitably typedef'd in "stdio.h".

Correct answer: TrueFILE is a structure type defined in <stdio.h>, holding the buffer, the position indicator and the state flags for a stream. Programs use it only through a FILE * and never look inside - its contents are the implementation’s business.

Q: Which of the given function differs from the statement’errno is not necessarily set on conversion error’?

Correct answer: strtod()strtod is the one that does report errors: on overflow or underflow it sets errno to ERANGE, and it also returns a pointer to the first unconverted character. The ato family - atoi, atof, atol - simply return 0 on failure and set nothing, which is why the strto functions should be preferred.

Q: Point out the error in the following program. #include <stdio.h> int main() { fprintf("Compscibits"); printf("%.ef", 2.0); return 0; }

Correct answer: Error: in fprintf() statementfprintf requires a stream as its first argument - fprintf(stdout, "..."). Called with only a string it is missing that argument, and the string is taken as the stream, which is a type error. Plain printf is the version that writes to stdout without being told.

Q: What will be the output of the program? #include <stdio.h> int main() { int i; char c; for(i=1; i<=5; i++) { scanf("%c", &c); /* given input is 'a' */ printf("%c", c); ungetc(c, stdin); } return 0; }

Correct answer: aaaaaungetc pushes the character back onto the input stream, so the next scanf reads the same character again. The loop therefore reads and prints the same a on all five passes, giving aaaaa. Only one character of pushback is guaranteed, which is all this needs.

Q: What will be the output of the program? #include <stdio.h> int main() { int i; char c; for(i=1; i<=5; i++) { scanf("%c", &c); /* given input is 'a' */ printf("%c", c); ungetc(c, stdin); } return 0; }

Correct answer: aaaaaungetc pushes the character back onto the input stream, so the next scanf reads the same character again. The loop therefore reads and prints the same a on all five passes, giving aaaaa. Only one character of pushback is guaranteed, which is all this needs.

Q: In the c library function void (*signal(int sig, void (*func)(int)))(int), which statement is true with respect to func?

Correct answer: func is a pointer to the functionRead the declaration outwards: void (*func)(int) makes func a pointer to a function taking an int and returning nothing - the handler to be installed. signal itself returns a pointer of the same kind, namely the previous handler, which is what makes the declaration so hard to read.

Q: If the result underflows, the function returns zero.

Correct answer: trueOn underflow - a result too small in magnitude to be represented - a maths function returns zero, and may set errno to ERANGE. That contrasts with overflow, where it returns HUGE_VAL.

Q: What is returned by the function localeconv()?

Correct answer: pointer to the current locationlocaleconv() returns a pointer to a struct lconv describing the conventions of the locale currently in force - decimal point, thousands separator, currency symbol and its placement. The structure is static, so its contents change when the locale is changed.

11.

What will be the output of the program?

#include <stdio.h>

int main()
{
    int i;
    char c;
    for(i=1; i<=5; i++)
    {
        scanf("%c", &c); /* given input is 'b' */
        ungetc(c, stdout);
        printf("%c", c);
        ungetc(c, stdin);
    }
    return 0;
}

A.bbbb
B.bbbbb
C.b
D.Error in ungetc statement.

Answer: C

The ungetc() function pushes the character c back onto the named input stream, which must be open for reading.

This character will be returned on the next call to getc or fread for that stream.

One character can be pushed back in all situations.

A second call to ungetc without a call to getc will force the previous character to be forgotten.

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12.

Which statement is true regarding abs() and labs()?

A.The abs() function is similar to the labs() function, except that the argument and the returned value each of them have type long int
B.The abs() function is not similar to the labs() function, except that the argument and the returned value in both functions have type long int
C.The abs() function is similar to the labs() function, except that the argument and the returned value each have type short int
D.The abs() function is not similar to the labs() function, except that the argument and the returned value in both function have type short int

Answer: A

Correct answer: The abs() function is similar to the labs() function, except that the argument and the returned value each of them have type long int

The two do the same thing for different types: abs takes and returns an int, and labs takes and returns a long int. (llabs was added for long long, and fabs handles floating point.)

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13.

FILE is a structure suitably typedef'd in "stdio.h".

A.True
B.False

Answer: A

Correct answer: True

FILE is a structure type defined in <stdio.h>, holding the buffer, the position indicator and the state flags for a stream. Programs use it only through a FILE * and never look inside - its contents are the implementation’s business.

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14.

Which of the given function differs from the statement’errno is not necessarily set on conversion error’?

A.atof()
B.atoi()
C.atol()
D.strtod()

Answer: D

Correct answer: strtod()

strtod is the one that does report errors: on overflow or underflow it sets errno to ERANGE, and it also returns a pointer to the first unconverted character. The ato family - atoi, atof, atol - simply return 0 on failure and set nothing, which is why the strto functions should be preferred.

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15.

Point out the error in the following program.

#include <stdio.h>

int main()
{
    fprintf("Compscibits");
    printf("%.ef", 2.0);
    return 0;
}

A.Error: unknown value in printf() statement
B.Error: in fprintf() statement
C.No error and prints "Compscibits"
D.No error and prints "2.0"

Answer: B

Correct answer: Error: in fprintf() statement

fprintf requires a stream as its first argument - fprintf(stdout, "..."). Called with only a string it is missing that argument, and the string is taken as the stream, which is a type error. Plain printf is the version that writes to stdout without being told.

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16.

What will be the output of the program?

#include <stdio.h>

int main()
{
    int i;
    char c;
    for(i=1; i<=5; i++)
    {
        scanf("%c", &c); /* given input is 'a' */
        printf("%c", c);
        ungetc(c, stdin);
    }
    return 0;
}

A.aaaa
B.aaaaa
C.Garbage value
D.Error in ungetc statement

Answer: B

Correct answer: aaaaa

ungetc pushes the character back onto the input stream, so the next scanf reads the same character again. The loop therefore reads and prints the same a on all five passes, giving aaaaa. Only one character of pushback is guaranteed, which is all this needs.

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17.

What will be the output of the program?

#include <stdio.h>

int main()
{
    int i;
    char c;
    for(i=1; i<=5; i++)
    {
        scanf("%c", &c); /* given input is 'a' */
        printf("%c", c);
        ungetc(c, stdin);
    }
    return 0;
}

A.aaaa
B.aaaaa
C.Garbage value.
D.Error in ungetc statement.

Answer: B

Correct answer: aaaaa

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18.

In the c library function void (*signal(int sig, void (*func)(int)))(int), which statement is true with respect to func?

A.func is a pointer to the function
B.func is pointer to sig
C.func is a static variable
D.func is a pointer that points to all type of data

Answer: A

Correct answer: func is a pointer to the function

Read the declaration outwards: void (*func)(int) makes func a pointer to a function taking an int and returning nothing - the handler to be installed. signal itself returns a pointer of the same kind, namely the previous handler, which is what makes the declaration so hard to read.

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19.

If the result underflows, the function returns zero.

A.true
B.false

Answer: A

Correct answer: true

On underflow - a result too small in magnitude to be represented - a maths function returns zero, and may set errno to ERANGE. That contrasts with overflow, where it returns HUGE_VAL.

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20.

What is returned by the function localeconv()?

A.current location value
B.past location value
C.pointer to the last location
D.pointer to the current location

Answer: D

Correct answer: pointer to the current location

localeconv() returns a pointer to a struct lconv describing the conventions of the locale currently in force - decimal point, thousands separator, currency symbol and its placement. The structure is static, so its contents change when the locale is changed.

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