Difference between revisions of "C-and-C++/C3/String-Library-Functions/English"

Library Functions in C

Learning Objectives

String Library Functions

We will do this with the help of some examples

System Requirements

Ubuntu Operating System version 11.10,

gcc Compiler Version 4.6.1

Introduction to the standard library funtions

These are the group of functions implementing operations on strings.

Various operations such as copying, concatenation, searching etc are supported.

String Library functions

Here we have the strncpy function

The syntax for this is strncpy(char str1, char str2, int n )

It copies first n characters of string str2 into string str1.

eg.

char strncpy(char hello, char world, 2);

The output will be

Wollo

Here we have Wo fromt the string 2 and rest of the characters from string 1

It will compare first n characters of string 2 with string 1

eg.

int strncmp(char ice, char icecream, int 2);

The output will be 0

Please open the Text Editor

Go to Applications – Accessories – Text Editor

I am going to show you some of the commonly used string functions.

I have already typed the program on the editor,

i will open it

Here we have the string length function

In this we will find the length of the string

These are the header files as stdio.h and string.h Make only one file which contain all the code / function.

This is our main function

char arr[] = "Icecream";

It stores a value 'Ashwini'

Then we have an integer variable len1

int len1 = strlen(arr);

the result will be stored in len1

printf("string = %s length = %d\n", arr, len1);

And this is our return statement

Ctrl, Alt and T keys simultaneously

Open the terminal window by pressing

Ctrl, Alt and T keys simultaneously on your keyboard

gcc strlen.c -o len

Type:

"gcc" space "strlen.c" space “-o” space “str1”.

Press Enter

./str1

./str1

Press Enter

Output

string = Ashwini, Length = 7

You can count here. 1,2,3,4,5,6, and 7

Here we have the string copy fuction

strcpy(target, source);

Here we have Ice in the source string, it will be copied to the target string

printf("source string = %s\n",source);

Please Switch back to the terminal

Come back to our terminal

gcc space strcpy.c space -o space str2

Press Enter

Type

./str2

Press Enter

Everywhere you change the file name and tell them to compile as before. Yes, i want an explanation?

* Ignore this, i deleted.

Output

source string = Ice

target string = Ice

Note that our filename is strcmp.c

In this we will comapre two strings

Here we have character variables as str1 and str2

char source[]= "World";

char target[]= "Hello";

Here we have interger variables as i and j

In this we will compare the string using the strcmp function

Here we compare str1 ie: 'Ice' with 'Hello'

The result is stored in i

In this we will compare string 2 ie: 'Cream' with 'Cream'

The result is stored in j

Then we print both the results

and this is our return statement

Please switch back to the terminal

Come back to our terminal.

gcc space strcmp.c space -o space str3

Press Enter

Type

./str3

The outpur is displayed as 1,0

Here we get 1

and here we get as 0

Let us come back to our slides

Let us summarize,

String library functions

strlen()

strcpy()

strcmp()

strncpy()

and strncmp()

Assignment

Write a C Program to concatenate String best and String bus.

Hint: strcat(char str1, char str2);

Also explore the other functions in string library.

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