C library - strcat() function

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The C Library strcat() function accepts two pointer variable as parameters(say dest, src) and, appends the string pointed to by src to the end of the string pointed to by dest. This function only concatenates the string data type. We cannot use any other data types such int, float, char, etc.

Syntax

Following is the syntax of the C library strcat() function −

char *strcat(char *dest_str, const char *src_str)

Parameters

This function accepts the following parameters −

• dest_str − 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_str − This is the string to be appended. This should not overlap the destination.

Return Value

This function returns a pointer to the resulting string i.e. dest.

Note that, the function dynamically combine strings during runtime.

Example 1

Following is the basic C library program that illustrates the code snippet on string concatenation using strcat() function.

#include <stdio.h>
#include <string.h>
int main() {
   char dest_str[50] = "C ";
   const char src_str[] = "JAVA";

   // Concatenate src_str to dest_str
   strcat(dest_str, src_str);

   // The result store in destination string
   printf("%s", dest_str); 
   return 0;
}

Output

On executing the above code, we get the following output−

Final destination string : |This is destinationThis is source|

Example 2

In the following example, we are using the strcpy() along with the strcat() function, to merge the new string ("point") with the existing string ("tutorials").

#include <stdio.h> 
#include <string.h> 
int main() 
{ 
   char str[100]; 
   
   // Copy the first string to the variable
   strcpy(str, "Tutorials"); 

   // String concatenation 
   strcat(str, "point"); 

   // Show the result
   printf("%s\n", str); 
   return 0; 
}

Output

The above code produces the following output−

Tutorialspoint

Example 3

While concatenating two different strings always requires two parameters, but here we are using integer values as parameters for strcat() that results in errors.

#include <stdio.h>
#include <string.h>
int main()
{   
    int x = 20;
    int y = 24;
    strcat(x, y);
    printf("%d", x);
    return 0;
}

Output

After executing the above code, we get the following result −

main.c: In function main:
main.c:7:12: warning: passing argument 1 of strcat makes pointer from integer without a cast [-Wint-conversion]
    7 |     strcat(x, y);
      |            ^
      |            |
      |            int
In file included from main.c:2:
/usr/include/string.h:149:39: note: expected char * restrict but argument is of type int
  149 | extern char *strcat (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~
main.c:7:15: warning: passing argument 2 of strcat makes pointer from integer without a cast [-Wint-conversion]
    7 |     strcat(x, y);
      |               ^
      |               |
      |               int
In file included from main.c:2:
/usr/include/string.h:149:70: note: expected const char * restrict but argument is of type int
  149 | extern char *strcat (char *__restrict __dest, const char *__restrict __src)
      |