Strcpy() in C

In C language many operations can be performed on a string. Characters in a sequence are known as string.

Note:   To use this function we must include the #include<string.h> header file in our program. This<string.h> header file contains all the required functions that are needed to perform operations on a string.

The string functions concerning operations they performed are given below :

• strlen()          gives the length of a string.
• strcmp()compares two strings.
• strcat()          concatenates two strings
• ()                   copies one string into another.
• strchr()         find the first occurrence of a given character in a string.
• strstr()           findthe occurrence of thefirst string in a string.
• strcasecmp()            without sensitivity to the case compares two strings.

These functionsare defined/inbuilt to reduce the complexity of performing the operations on a string.

1.strcpy()
strcpyis the abbreviationfor the string copy. This function is mainly used to copy one string into another string and provide a null character to terminate the string. The strings are the source string and destination string.
i.e, the content of the source string copied into the destination string.

Syntax:

strcpy(destination string , source string);

Or

char* strcpy(char* destination, const char* source);

• From syntax, we can say that the source string is after the destination string.
• When u see the second syntax the question may arise why const keyword at source string? This is because in the whole process we are not modifying the source we are simply coping the content in the source string to the destination string.

Important Points:

• Compare to the length of the source string the length of the destinations string should be greater than or equal.
• In this function when coping source string to destination string then the source string includes the null character.

Example 1:

For example, consider the length of the destination string is 5 and the source string is 10. Then, from the source string, only 5 characters will be copied into the destination string, and the remaining 10 characters won’t be copied and will be truncated.

char a[10]=”javatpoint”;
char b[5];
strcpy(b,a);

Output:

error

Example 2:

For example, consider the length of the destination string is10 and the source string is 10. Then, 10 characters are copied tothe destination string.

char a[10]=”javatpoint”;
char b[10];
strcpy(b,a);

Output:

javatpoint

Program

#include<stdio.h>
#include<string.h>
int main() {
char a[10]=”javatpoint”;
char b[10];
printf(“%s\n”,strcpy(b,a));//strcpy function
return 0;
}

Output:

javatpoint

Note:      strcpy returns the pointer to the first character of the string which is copied to the destination. Then the whole string will be printed on the screenby using the %s.

We can also chain together a series of strcpy calls i.e,the strcpy function is stored or performed by another strcpy function. Like nested strcpy function. The example is shown below.

Program

#include<stdio.h>
#include<string.h>
int main() {
char a[10]=”javatpoint”;
char b[10];
char c[10];
strcpy(c,strcpy(b,a))//strcpy within strcpy
printf(“%s\n%s\n”,b,c);
return 0;
}

Output:

Javatpoint
javatpoint

If the length of the string pointed by the source string is greater than the length of the character array destination string then it will be undefined behaviour as shown in the below program.

Program

#include<stdio.h>
#include<string.h>
int main() {
char a[10]=”javatpoint”;
char b[5];
printf(“%s\n”,strcpy(b,a));//strcpy function
return 0;
}

Output:

Undefined behavior

To avoid this we can call the strncpy function instead of strcpy.strncpy is the abbreviation of string n copy. n number of characters are copied by using this function. The drawback of the strcpy() is overcome by the strncpy().

Syntax:

strncpy(destination string , source string,siZeof(destination));

Program

#include<stdio.h>
#include<string.h>
int main() {
char a[10]=”javatpoint”;
char b[5];
strncpy(b,a,sizeof(b))//strncpy function
return 0;
printf(“%s\n”,b);
}

Output:

javat

strncpy will leave the string in its destination without a terminating null character if the size of the source is equal to or greater than the size ofthe destination. For this purpose, we add an extra line in our program as shown in below.

Program

#include<stdio.h>
#include<string.h>
int main() {
char a[11]=”javatpoint”;
char b[11];
strncpy(b,a,sizeof(b))//strncpy function
b[sizeof(b)-1]=’\0’;//add null character
return 0;
printf(“%s\n”,b);
}

Output:

Javatpoint

In the above program, we have added the null character in the destination.