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The strcat() is a string manipulation function defined in the string.h header file, which works on a string which is stored in a c-style char array. This function is used to add or concatenate two strings by appending a string at the end of another string.

Signature of strcat() function

char * strcat ( char * destination, const char * source )

• A source is a string(a string which is stored in a c-style char array) passed to this function, whose characters are to be appended at the end of another string destination.
• This function appends the character of source string at the end of the characters present in the destination string and returns a char[] array pointer, pointing to the destination string containing the addition of both string values.

Example of strcat() function

In the upcoming code, we are calling strcat() function, to add the content of one string named src at the end of characters present in another string named dest, both string values are contained in a char[] array and are passed as a parameter to the strcat() function.

// Program to concatenate values in two char array with string values */

#include<iostream>
#include<cstring>

using namespace std;

int main()
{
char dest[10] = "Hello";
char src[10] = "World";
cout<<"The value in destination string : " <<dest << "\n";
cout<<"The second in source string : " <<src << "\n";

strcat(dest,src);
cout<<"Concatenated strings : " << dest;

return 0;
}

Output is -

First  String value : Hello
Second String value : World
Concatenated strings : HelloWorld

• The first char[] array i.e. dest is initialized with a string value Hello and the second char[] array i.e. dest is initialized with the value World.
• The function strcat() appends the string value in the src char[] array at the end of characters present in the second char[] array i.e. dest, both passed as parameter to strcat() function.

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Adding two strings without using strcat()

Let's create a program which appends the characters in one string at the end of another string without using strcat() function.

// Program to append one string at the end of another string withut strcat() function 


#include<iostream>
#include<cstring>

using namespace std;

int main()
{
char dest[20] = "Hello";
char src[10] = "World";

cout<< "The value in dest string : " << dest << "\n";
cout<< "The second in src string : " << src << "\n";

int len1 = strlen(dest);
int len2 = strlen(src);

cout<< "Length of characters in dest string : " << len1 << "\n";
cout<< "Length of characters in src string : " << len2 << "\n";

for(int i=0;i<len2; i++)
{
	dest[len1] = src[i];
	len1 = len1 + 1 ;
}
dest[len1]='\0';

cout<< "Concatenated strings : " << dest;

return 0;
}

Output is :

The value in dest string : Hello
The second in src string : World
Length of characters in dest string : 5
Length of characters in src string : 5
Concatenated strings : HelloWorld

• The first char[] array i.e. dest is initialized with a string value Hello and the second char[] array i.e. dest is initialized with the value World.
• Next, we have calculated the total length of characters actually present in each char[] array, by using strlen() function.
• Next, we have manually appended each character taken from src char[] array to the end of dest char[].

Note: - The function strlen returns the total number of characters actually present in the char[] and not the total number of character it can hold.

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C++ strncat() function >

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