Difference Between strcpy() and strcat() Function in C

String manipulation is an essential concept in C programming. The C standard library provides functions like strcpy() and strcat() to copy and concatenate strings efficiently. In this post, we’ll examine how strcpy() and strcat() are used as well as some of their main distinctions.

The strcpy() Function in C

The strcpy() function inserts the whole string (including the null terminator) that is referenced by the source into the destination array.

The syntax is:

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

Let’s look at an example:

#include <stdio.h>
#include <string.h>

int main() {

  char source[20] = "Hello World";
  char destination[20];

  strcpy(destination, source);

  printf("Source string: %s\n", source);
  printf("Destination string: %s\n", destination);
  
  return 0;
}

Output:
Source string: Hello World
Destination string: Hello World

Here, the source string “Hello World” is copied into the destination array using strcpy().

Some key points about strcpy():

• Overwrites destination string fully even if arrays overlap
• Faster than strcat() in most cases
• Risk of buffer overflow if destination is too small

The strcat() Function in C

The strcat() function concatenates two strings by appending a copy of source to the end of destination.

The syntax is:

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

Let’s look at an example:

#include <stdio.h>
#include <string.h>

int main() {

  char str1[20] = "Hello";
  char str2[20] = "World";

  strcat(str1, str2);

  printf("str1 before concat: %s\n", str1);
  printf("str2 string: %s\n", str2);
  printf("Concatenated string: %s\n", str1);

  return 0;
}

Output:
str1 before concat: Hello
str2 string: World
Concatenated string: HelloWorld

Here, strcat() appends str2 to str1, resulting in the concatenated string.

Key properties of strcat():

• The destination must have a null terminator before concatenating
• Original destination value is not overwritten, only appended to
• Risk of buffer overflow if destination buffer is too small

Common Example

#include <stdio.h>
#include <string.h>

int main() {
    char name1[10] = "DataFlair";
    char name2[10] = "Rohan"; // Changed from "John" to "Rohan"
    char name3[10];

    strcpy(name3, name1);
    printf("%s\n", name3); // Output: DataFlair

    strcat(name1, name2);
    printf("%s\n", name1); // Output: DataFlairRohan

    return 0;
}

Explanation:

• Two character arrays, name1 and name2, are declared and initialized with “DataFlair” and “Rohan,” respectively.
• An empty character array name3 is declared.
• The strcpy function copies name1 to name3, resulting in name3 containing “DataFlair.”
• The printf function displays the content of name3 (“DataFlair”).
• The strcat function concatenates name2 to the end of name1, making name1 “DataFlairRohan.”
• The printf function displays the content of name1 (“DataFlairRohan”).
• The program exits with a status code of 0.

#include <stdio.h>
#include <string.h>

int main() {

  char source[100] = "This is a source string";
  char dest[100];
  
  // Copy source to dest using strcpy()
  strcpy(dest, source);
  
  // Concatenate additional string using strcat()
  strcat(dest, " - Extra appended text"); 
  
  printf("Source string: %s\n", source);
  printf("Destination string: %s\n", dest);
  
  return 0;
}

Output:

Source string: This is a source string
Destination string: This is a source string – Extra appended text

In this program:

• strcpy() is used to copy the source string into destination string.
• strcat() is then used to append additional text to the destination string.
• Finally, both source and destination strings are printed to demonstrate the result.

When to Use Each Function

Based on their behavior, here are some guidelines on when to use each one:

• Use strcpy() when you need to completely replace the destination string
• Use strcat() when you need to append two strings by concatenating
• Use strcpy() in time-critical sections for better performance
• Use strcat() when maintaining null terminated substrings is required

Key Differences Between C strcpy() and strcat()

Conclusion

In summary, strcpy() and strcat() allow efficient string manipulation in C but have some key differences. strcpy() overwrites the destination while strcat() appends to it. Keeping their exact behavior in mind helps us pick the right function and use it safely by managing null termination and buffers.