stdlib.h

Question 1

What is srand()?

Declaration:

void srand(unsigned int seed);

Answer 1

This function seeds the random number generator used by the function rand. Seeding srand with the same seed will cause rand to return the same sequence of pseudo-random numbers. If srand is not called, rand acts as if srand(1) has been called.

No value is returned.

Question 2

What is calloc()?

Declaration:

void *calloc(size_t nitems, size_t size);

Answer 2

Allocates the requested memory and returns a pointer to it. The requested size is nitems each size bytes long (total memory requested is nitems*size). The space is initialized to all zero bits.

On success a pointer to the requested space is returned. On failure a null pointer is returned.

Question 3

What is wcstombs()?

Declaration:

size_t wcstombs(char *str, const wchar_t *pwcs, size_t n);

Answer 3

Converts the codes stored in the array pwcs to multibyte characters and stores them in the string str. It copies at most n bytes to the string. If a multibyte character overflows the n constriction, then none of that multibyte character’s bytes are copied. Conversion stops when it reaches the null character or n bytes have been written to the string. The null character is stored in the string, but is not counted in the return value.

If an invalid code is reached, the value -1 is returned. Otherwise the number of bytes stored in the string is returned not including the terminating null character.

Question 4

What is strtod()?

Declaration:

double strtod(const char *str, char **endptr);

Answer 4

The string pointed to by the argument str is converted to a floating-point number (type double). Any initial whitespace characters are skipped (space, tab, carriage return, new line, vertical tab, or formfeed). The number may consist of an optional sign, a string of digits with an optional decimal character, and an optional e or E followed by a optionally signed exponent. Conversion stops when the first unrecognized character is reached.
The argument endptr is a pointer to a pointer. The address of the character that stopped the scan is stored in the pointer that endptr points to.

On success the converted number is returned. If no conversion can be made, zero is returned. If the value is out of range of the type double, then HUGE_VAL is returned with the appropriate sign and ERANGE is stored in the variable errno. If the value is too small to be returned in the type double, then zero is returned and ERANGE is stored in the variable errno.

Question 5

What is div()?

Declaration:

div_t div(int numer, int denom);

Answer 5

Divides numer (numerator) by denom (denominator). The result is stored in the structure div_t which has two members:

int qout;
int rem;

Where quot is the quotient and rem is the remainder. In the case of inexact division, quot is rounded down to the nearest integer. The value numer is equal to quot * denom + rem.

The value of the division is returned in the structure.

Question 6

What is atol()?

Declaration:

long int atol(const char *str);

Answer 6

The string pointed to by the argument str is converted to a long integer (type long int). Any initial whitespace characters are skipped (space, tab, carriage return, new line, vertical tab, or formfeed). The number may consist of an optional sign and a string of digits. Conversion stops when the first unrecognized character is reached.

On success the converted number is returned. If the number cannot be converted, then 0 is returned.

Question 7

What is rand()?

Declaration:

int rand(void);

Answer 7

Returns a pseudo-random number in the range of 0 to RAND_MAX.

The random number is returned.

Question 8

What is atoi()?

Declaration:

int atoi(const char *str);

Answer 8

The string pointed to by the argument str is converted to an integer (type int). Any initial whitespace characters are skipped (space, tab, carriage return, new line, vertical tab, or formfeed). The number may consist of an optional sign and a string of digits. Conversion stops when the first unrecognized character is reached.

On success the converted number is returned. If the number cannot be converted, then 0 is returned.

Question 9

What is mblen()?

Declaration:

int mblen(const char *str, size_t n);

Answer 9

Returns the length of a multibyte character pointed to by the argument str. At most n bytes will be examined.
If str is a null pointer, then zero is returned if multibyte characters are not state-dependent (shift state). Otherwise a nonzero value is returned if multibyte character are state-dependent.

If str is not null, then the number of bytes that are contained in the multibyte character pointed to by str are returned. Zero is returned if str points to a null character. A value of -1 is returned if str does not point to a valid multibyte character.

Question 10

What is labs()?

Declaration:

long int labs(long int x);

Answer 10

Returns the absolute value of x. Not that in two’s compliment that the most maximum number cannot be represented as a positive number. The result in this case is undefined.

The absolute value is returned.

Question 11

What is malloc()?

Declaration:

void *malloc(size_t size);

Answer 11

Allocates the requested memory and returns a pointer to it. The requested size is size bytes. The value of the space is indeterminate.

On success a pointer to the requested space is returned. On failure a null pointer is returned.

Question 12

What is system()?

Declaration:

int system(const char *string);

Answer 12

The command specified by string is passed to the host environment to be executed by the command processor. A null pointer can be used to inquire whether or not the command processor exists.

If string is a null pointer and the command processor exists, then zero is returned. All other return values are implementation-defined.

Question 13

What is bsearch()?

Declaration:

void *bsearch(const void *key, const void *base, size_t nitems, size_t size, int (*compar)(const void *, const void *));

Answer 13

Performs a binary search. The beginning of the array is pointed to by base. It searches for an element equal to that pointed to by key. The array is nitems long with each element in the array size bytes long.

The method of comparing is specified by the compar function. This function takes two arguments, the first is the key pointer and the second is the current element in the array being compared. This function must return less than zero if the compared value is less than the specified key. It must return zero if the compared value is equal to the specified key. It must return greater than zero if the compared value is greater than the specified key.

The array must be arranged so that elements that compare less than key are first, elements that equal key are next, and elements that are greater than key are last.

If a match is found, a pointer to this match is returned. Otherwise a null pointer is returned. If multiple matching keys are found, which key is returned is unspecified.

Question 14

What is abort()?

Declaration:

void abort(void);

Answer 14

Causes an abnormal program termination. Raises the SIGABRT signal and an unsuccessful termination status is returned to the environment. Whether or not open streams are closed is implementation-defined.

No return is possible.

Question 15

What is mbtowc()?

Declaration:

int mbtowc(whcar_t *pwc, const char *str, size_t n);

Answer 15

Examines the multibyte character pointed to by the argument str. The value is converted and stored in the argument pwc if pwc is not null. It scans at most n bytes.

If str is a null pointer, then zero is returned if multibyte characters are not state-dependent (shift state). Otherwise a nonzero value is returned if multibyte character are state-dependent.

If str is not null, then the number of bytes that are contained in the multibyte character pointed to by str are returned. Zero is returned if str points to a null character. A value of -1 is returned if str does not point to a valid multibyte character.

Question 16

What is strtol()?

Declaration:

long int strtol(const char *str, char **endptr, int base);

Answer 16

The string pointed to by the argument str is converted to a long integer (type long int). Any initial whitespace characters are skipped (space, tab, carriage return, new line, vertical tab, or formfeed). The number may consist of an optional sign and a string of digits. Conversion stops when the first unrecognized character is reached.
If the base (radix) argument is zero, then the conversion is dependent on the first two characters. If the first character is a digit from 1 to 9, then it is base 10. If the first digit is a zero and the second digit is a digit from 1 to 7, then it is base 8 (octal). If the first digit is a zero and the second character is an x or X, then it is base 16 (hexadecimal).

If the base argument is from 2 to 36, then that base (radix) is used and any characters that fall outside of that base definition are considered unconvertible. For base 11 to 36, the characters A to Z (or a to z) are used. If the base is 16, then the characters 0x or 0X may precede the number.

The argument endptr is a pointer to a pointer. The address of the character that stopped the scan is stored in the pointer that endptr points to.

On success the converted number is returned. If no conversion can be made, zero is returned. If the value is out of the range of the type long int, then LONG_MAX or LONG_MIN is returned with the sign of the correct value and ERANGE is stored in the variable errno.

Question 17

What is free()?

Declaration:

void free(void *ptr);

Answer 17

Deallocates the memory previously allocated by a call to calloc, malloc, or realloc. The argument ptr points to the space that was previously allocated. If ptr points to a memory block that was not allocated with calloc, malloc, or realloc, or is a space that has been deallocated, then the result is undefined.

No value is returned.

Question 18

What is struct div_t?

Answer 18

The structure returned by the div function.

Question 19

What is atof()?

Declaration:

double atof(const char *str);

Answer 19

The string pointed to by the argument str is converted to a floating-point number (type double). Any initial whitespace characters are skipped (space, tab, carriage return, new line, vertical tab, or formfeed). The number may consist of an optional sign, a string of digits with an optional decimal character, and an optional e or E followed by a optionally signed exponent. Conversion stops when the first unrecognized character is reached.

On success the converted number is returned. If no conversion can be made, zero is returned. If the value is out of range of the type double, then HUGE_VAL is returned with the appropriate sign and ERANGE is stored in the variable errno. If the value is too small to be returned in the type double, then zero is returned and ERANGE is stored in the variable errno.

Question 20

What is strtoul()?

Declaration:

unsigned long int strtoul(const char *str, char **endptr, int base);

Answer 20

The string pointed to by the argument str is converted to an unsigned long integer (type unsigned long int). Any initial whitespace characters are skipped (space, tab, carriage return, new line, vertical tab, or formfeed). The number may consist of an optional sign and a string of digits. Conversion stops when the first unrecognized character is reached.

If the base (radix) argument is zero, then the conversion is dependent on the first two characters. If the first character is a digit from 1 to 9, then it is base 10. If the first digit is a zero and the second digit is a digit from 1 to 7, then it is base 8 (octal). If the first digit is a zero and the second character is an x or X, then it is base 16 (hexadecimal).

If the base argument is from 2 to 36, then that base (radix) is used and any characters that fall outside of that base definition are considered unconvertible. For base 11 to 36, the characters A to Z (or a to z) are used. If the base is 16, then the characters 0x or 0X may precede the number.

The argument endptr is a pointer to a pointer. The address of the character that stopped the scan is stored in the pointer that endptr points to.

On success the converted number is returned. If no conversion can be made, zero is returned. If the value is out of the range of the type unsigned long int, then ULONG_MAX is returned and ERANGE is stored in the variable errno.

Question 21

What is wctomb()?

Declaration:

int wctomb(char *str, wchar_t wchar);

Answer 21

Examines the code which corresponds to a multibyte character given by the argument wchar. The code is converted to a multibyte character and stored into the string pointed to by the argument str if str is not null.

If str is a null pointer, then zero is returned if multibyte characters are not state-dependent (shift state). Otherwise a nonzero value is returned if multibyte character are state-dependent.

If str is not null, then the number of bytes that are contained in the multibyte character wchar are returned. A value of -1 is returned if wchar is not a valid multibyte character.

Question 22

What is getenv()?

Declaration:

char *getenv(const char *name);

Answer 22

Searches for the environment string pointed to by name and returns the associated value to the string. This returned value should not be written to.

If the string is found, then a pointer to the string’s associated value is returned. If the string is not found, then a null pointer is returned.

Question 23

What is typedef wchar_t?

Answer 23

An integer type of the size of a wide character constant.

Question 24

What is realloc()?

Declaration:

void *realloc(void *ptr, size_t size);

Answer 24

Attempts to resize the memory block pointed to by ptr that was previously allocated with a call to malloc or calloc.

The contents pointed to by ptr are unchanged. If the value of size is greater than the previous size of the block, then the additional bytes have an undeterminate value. If the value of size is less than the previous size of the block, then the difference of bytes at the end of the block are freed. If ptr is null, then it behaves like malloc.

If ptr points to a memory block that was not allocated with calloc or malloc, or is a space that has been deallocated, then the result is undefined. If the new space cannot be allocated, then the contents pointed to by ptr are unchanged. If size is zero, then the memory block is completely freed.

On success a pointer to the memory block is returned (which may be in a different location as before). On failure or if size is zero, a null pointer is returned.

Question 25

What is qsort()?

Declaration:

void qsort(void *base, size_t nitems, size_t size, int (*compar)(const void *, const void*));

Answer 25

Sorts an array. The beginning of the array is pointed to by base. The array is nitems long with each element in the array size bytes long.

The elements are sorted in ascending order according to the compar function. This function takes two arguments. These arguments are two elements being compared. This function must return less than zero if the first argument is less than the second. It must return zero if the first argument is equal to the second. It must return greater than zero if the first argument is greater than the second.

If multiple elements are equal, the order they are sorted in the array is unspecified.

No value is returned.

Example:

#include
 #include
 #include

int main(void)
{
char string_array[10][50]={“John”,
“Jane”,
“Mary”,
“Rogery”,
“Dave”,
“Paul”,
“Beavis”,
“Astro”,
“George”,
“Elroy”};

/* Sort the list */
qsort(string_array,10,50,strcmp);

/* Search for the item “Elroy” and print it */
printf(“%s”,bsearch(“Elroy”,string_array,10,50,strcmp));

return 0;
}

Question 26

What is exit()?

Declaration:

void exit(int status);

Answer 26

Causes the program to terminate normally. First the functions registered by atexit are called, then all open streams are flushed and closed, and all temporary files opened with tmpfile are removed. The value of status is returned to the environment. If status is EXIT_SUCCESS, then this signifies a successful termination. If status is EXIT_FAILURE, then this signifies an unsuccessful termination. All other values are implementation-defined.

No return is possible.

Question 27

What is typedef size_t?

Answer 27

The unsigned integer result of the sizeof keyword.

Question 28

What are EXIT_FAILURE and EXIT_SUCCESS?

Answer 28

Values for the exit function to return termination status.

Question 29

What is atexit()?

Declaration:

int atexit(void (*func)(void));

Answer 29

Causes the specified function to be called when the program terminates normally. At least 32 functions can be registered to be called when the program terminates. They are called in a last-in, first-out basis (the last function registered is called first).

On success zero is returned. On failure a nonzero value is returned.

Question 30

What is RAND_MAX?

Answer 30

The maximum value returned by the rand function.

Question 31

What is abs()?

Declaration:

int abs(int x);

Answer 31

Returns the absolute value of x. Note that in two’s compliment that the most maximum number cannot be represented as a positive number. The result in this case is undefined.

The absolute value is returned.

Question 32

What is NULL?

Answer 32

The value of a null pointer constant.

Question 33

What is struct ldiv_t?

Answer 33

The structure returned by the ldiv function.

Question 34

What is MB_CUR_MAX?

Answer 34

The maximum number of bytes in a multibyte character set which cannot be larger than MB_LEN_MAX.

Question 35

What is mbstowcs()?

Declaration:

size_t mbstowcs(schar_t *pwcs, const char *str, size_t n);

Answer 35

Converts the string of multibyte characters pointed to by the argument str to the array pointed to by pwcs. It stores no more than n values into the array. Conversion stops when it reaches the null character or n values have been stored. The null character is stored in the array as zero but is not counted in the return value.

If an invalid multibyte character is reached, then the value -1 is returned. Otherwise the number of values stored in the array is returned not including the terminating zero character.

Question 36

What is ldiv()?

Declaration:

ldiv_t ldiv(long int numer, long int denom);

Answer 36

Divides numer (numerator) by denom (denominator). The result is stored in the structure ldiv_t which has two members:

long int qout;
long int rem;

Where quot is the quotient and rem is the remainder. In the case of inexact division, quot is rounded down to the nearest integer. The value numer is equal to quot * denom + rem.

The value of the division is returned in the structure.