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strcat() in C

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C strcat() function appends the string pointed to by src to the end of the string pointed to by dest. It will append a copy of the source string in the destination string. plus a terminating Null character. The initial character of the string(src) overwrites the Null-character present at the end of the string(dest).

It is a predefined string handling function under string library <string.h> in c and <cstring> in C++.


char *strcat(char *dest, const char *src);

Parameters: The method accepts the following parameters:

  • dest: This is a pointer to the destination array, which should contain a C string, and should be large enough to contain the concatenated resulting string.
  • src: This is the string to be appended. This should not overlap the destination.

Return value:

  • The strcat() function returns dest, the pointer to the destination string.
String Concatenate



Input: src = "ForGeeks"
       dest = "Geeks"
Output: "GeeksForGeeks"

Input: src = "World"
       dest = "Hello "
Output: "Hello World"

Below is the C/C++ program to implement the above approach:


// C program to implement
// the above approach
#include <stdio.h>
#include <string.h>
// Driver code
int main()
    // Define a temporary variable
    char example[100];
    // Copy the first string into
    // the variable
    strcpy(example, "Geeks");
    // Concatenate this string
    // to the end of the first one
    strcat(example, "ForGeeks");
    // Display the concatenated strings
    printf("%s\n", example);
    return 0;



The behavior of strcat() is undefined if:

  • the destination array is not large enough for the contents of both src and dest and the terminating null character
  • if the string overlaps.
  • if either dest or src is not a pointer to a null-terminated byte string.
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Last Updated : 11 Mar, 2023
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