c standard lib ref

8/13/2019 C Standard Lib Ref

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C Programming


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Content

Appreciate C standard libraries

Appreciate and use standard I/O library

Appreciate and use character type library

The contents here are for Aricent Group internal training purposes only and do not carry any commercial value 2Restricted Aricent Group 2011

pprec a e an use ma ema cs rary

Appreciate and use standard utility library


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Standard Library What is meant by standard library?

It has header files and library files of standard functions e.g printf, scanf.

What is there in a header file?

It usually contains the prototypes of different functions, definition of macros and prototype

declaration of user defined data types.

What is there in Library files?


The definitions of the functions and variables

Is standard library compiler dependant?

Yes , though most of the functions are provided by every compiler , yet there are some functionsare supported on one platform, and not on other


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stdio.h stdio.h provides many input/output functions in C .

printf and scanf are two functions which are used heavily in c for

input/output.

printf and scanf use different conversion specifiers for different

data types .e.g. %c is used for character input/output while %d is


use or n eger npu ou pu .

Following table gives the summary of conversion specifiers for

different data types to print using printf and to get as input using

scanf.


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Conversion specifiers table in C

%d, %i Integer decimal number

%o Unsigned octal number%x, or %X Hexadecimal number , using

a,b,c,d,e,f or A,B,C,D,E,F

%u Unsigned decimal number

Conversion specifier Data Type

Restricted Aricent Group 2011The contents here are for Aricent Group internal training purposes only and do not carry any commercial value 5Restricted Aricent Group 2011

%cInt;unsigned single character

%s char *; print characters from the stringuntil '\0'

is found

%f double

%p Pointer variable


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Stdio.h

Whats the difference between sprintf and printf ?

printf writes the output on the console while sprintf writes the output

in some string.

What is the difference between sscanf and scanf?

scanf takes the input from the keybord or standard input device and


stores those values in to some variables, while sscanf takes values

from some string and stores them in the variables

Program on the next slide illustrate the working of sscanf and sprintf. Go through itseeing the comments.


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Sprintf and sscanf-example

#include

int main()

{

float f1=766.98;

char c1='z';

int i1=212;

int i4;

char c2;


float f2;char string1[30];

char string[30];

sprintf(string,"%d %f %s",i1,f1,"amit"); /* here values of i1,f1 and amit

will be copied in the string*/

sscanf(string,"%d%f%s",&i4, &f2, string1); /* here values are read back from string and theyare copied in i4, f2 and string1 */

printf("string is: %s\n",string);

printf("\nafter scanf we got %d %f %s\n ",i4,f2,string1);

return 0;

}


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ctype.h Functions in ctype.h checks the type of character or converts its type from one type to

another. Let us consider each of them

isalnum(int c ) // It checks whether a character is alphanumeric or not?

isalpha(int c) // checks whether a character is alphabetic or not iscntrl(int c ) // checks whether a character is control character or not

isdigit(int c) // checks whether a character is digit or not

isgraph(int c) // checks whether the character is printable character or

not (except space)


islower(int c) // checks whether the character is lowercase Englishcharacter or not

isupper(int c) // checks whether the character is uppercase English

character or not

isspace(int c) // checks whether the character is space or not

isxdigit(int c) // checks whether the character is hexadecimal digit or not i.e if character is any of {0,1,.9, A, B, C, D, E, F, a,b,c,d,e,f } or not

tolower(int c) // it converts the character to lowercase if possible otherwise result is input

character itself

toupper(int c) // It converts the character to uppercase if possible otherwise result is input

character itself


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ctype.h - ExampleFollowing program illustrate the working of two functions of ctype .h , toupper and

tolower. All other functions can be used in same way. Program takes a string and

first converts all of it characters in lowercase letters and then in uppercase letters.

int main (){

char *str = "Moral indignation is jealousy with a halo. - H. G. Wells";

char *p;

rintf "Ori inal strin : \"%s\"\n", str ;


printf("After tolower: \"");for (p = str; *p; p++)

printf("%c", tolower (* p));

printf("\"\n");

printf("After toupper: \"");

for (p = str; *p; p++)printf("% c", toupper (* p));

printf ("\"\n");

return 0;

}


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math.h As the name suggests math.h have the functions related to mathematical Functions.

Some of them have been listed here with their prototypes. The names of most of the

functions describe the functionality of them. However some description is given for

clarification.

double sin(double x) // x is in radian here. It returns the sin value of x

double cos(double x) // cos value is returned


double sqrt(double x) // square root value of x is obtained

double exp(double x) // It returns value of e ( base of natural logarithm) raised to

the power x

double pow(double x,double y) // It returns value of x raised to the power y


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math.h Following program just uses above mentioned functions on specific number for

illustration.

#include

#include

int main()

{

double d=9.7;

rintf "the sin value of the numer is =%f\n",sin d ;


printf("the cos value of the numer is =%f\n",cos(d));printf("the square root value of the numer is =%f\n",sqrt(d));

printf("the value of the 'e' raised to the power %f is =%f\n",d,exp(d));

printf("the value of the 2.5 raised to the power is =%f\n",pow(2.5,d));

return 0;

}


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stdlib.h

stdlib.h is the header of the general purpose standard library of C programminglanguage which includes functions involving memory allocation, process control,conversions and others.

Member Constants

The stdlib.h and stddef.h header files define the macro NULL, which yields a nullpointer constant, and represents a pointer value that is guaranteed not to point to avalid address in memory.


, ,

cast to a void * pointer:

#define NULL 0

#define NULL 0L

#define NULL ((void *) 0)


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stdlib.h

Member Data Types

A data type called size_t is defined in the stdlib.h library, which is used to

represent the size of an object.

Library functions that take sizes expect them to be of type size_t, and the sizeof


opera or eva ua es o s ze_ .

The actual type of size_t is platform-dependent; a common mistake is to

assume size_t is the same as unsigned int, which can lead to programming

errors.


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stdlib.h Some of the very important functions provided by stdlib.h are as follows atoi() // It converts a string to a integer like 123 will be converted 123 (read as

an integer).

itoa() // It does the reverse i.e. it converts the integer to the string

rand() // rand function return the random number between 0 to RAND_MAX.

Value of RAND_MAX depends on the library. However it is assumed at


srand() // If we use rand() function in isolation it will generate same sequence of

random numbers. So to get different sequence every time we use srand()

along with rand() . srand takes seed value as an argument. If seed value

is different then sequence of numbers will be different. This thing is

explained with the help of the program in coming slide.

See the examples in coming slide for illustration of these functions.


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stdlib.h Example ( atoi() function)int main()

{

int result;

char *test1 = "310";

char *test2 = "No Number";

result = atoi (test1);

" "


, .

result = atoi(test2); // Here result is unpredictable as atoi doesnt

check for errors.

printf("Test2 is %d\n", result);

}


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Stdlib.h Example ( rand and srand

function)int dieroll ()

{

return ((rand () % 6) + 1); // dieroll function returns the random value between 1- 6

whenever it is called}

int main ()

{


, ,

for (nd = 0; nd < 3; nd++)

{

die = dieroll (); // using the loop, three random values are generated every time theprogram is run. But these are repeated between the calls of the program . E.g. if4,1,3 is the pattern in first run of the program, that would be repeated in secondrun, third run so on.

total += die;

printf (" Die roll %d: %d\n", nd + 1, die);

}

printf ("\nThe total of the three dice is %d.\n", total);

}


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Rand and srandWe can remove the anomaly in previous program using srand function shown below.

int dieroll ()

{

return ((rand () % 6) + 1);

}int main ()

{

int total = 0, die, nd;

Here time(0) function is returning new

value each time the program is calledand that new value is passed as an

argument to srand.The srand() function

sets its argument as the seed for a new

Sequence of pseudo-random integers


srand(time(0));

for (nd = 0; nd < 3; nd++)

{

die = dieroll ();

total += die;

printf (" Die roll %d: %d\n", nd + 1, die);

}

printf ("\nThe total of the three dice is %d.\n", total);

return 0;

}

.

These sequences are repeatable bycalling srand() with the same seed value.

But since our seed value is different

each time we shall get different values

every time.


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content/materials in the slides are of a general nature and are not intended to address the specific circumstances of any particular

individual or entity. The material may provide links to internet sites (for

the convenience of users) over which Aricent Group has no control and

Disclaimer


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acknowledge sources of materials wherever traceable to an individual or

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