Imagine you have a bunch of toys, and you want to put them in a toy box. You could do it one by one, but that would take a long time. Instead, you can use a magic machine that copies all your toys and puts them in the toy box for you. In C programming, the C strcpy() function works like that magic machine. It copies a string of characters from one place in your program’s memory to another place.

A string is just a sequence of characters, like a word or a sentence.

In C, a string is actually an array of characters, where each character is stored in a consecutive memory location.

The C strcpy() function is a built-in function in C that allows you to copy a string from one memory location to another. Its full name is “string copy”, and it is declared in the standard C library header file string.h

Prerequisites

A basic but well-rounded understanding of C programming. You can acquire these by checking out the following posts:

Here is an example of how you might use strcpy() function:

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

int main() {
  char source[] = "Hello, Roland!";
  char destination[20];

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

  return 0;
}

In this code, we have two-character arrays: source and destination.

The source is initialized with the string “Hello, Roland!”, and the destination is empty.

The strcpy() function is called with two arguments: the first argument is the destination string(destination), and the second argument is the source string (source).

When strcpy() is called, it copies the contents of source to destination, so that destination now contains the same string as source.

After the call to strcpy(), the program prints out the contents of source and destination.

Output:

Source string: Hello, Roland!
Destination string: Hello, Roland!

The Importance of Creating the C strcpy() Function without Libraries

Learning how to create the C strcpy() function from scratch without using any library is a valuable exercise for several reasons.

First, it helps you gain a deeper understanding of how the C language works and how strings are handled in C.

By creating your own implementation of strcpy(), you will gain insight into the memory management of strcpy(), you will gain insight into the memory management techniques used in C, and how arrays are handled in C.

Second, it is a great exercise in problem-solving and critical thinking. By attempting to create the strcpy() function from scratch, you will need to think carefully about how to manipulate memory and iterate over arrays to achieve the desired result.

This kind of thinking is valuable in many areas of programming and can help you become a better programmer overall.

Finally, creating your own implementation of strcpy() is a fun and challenging exercise that can help you become more confident in your programming skills.

It is like solving a puzzle – once you have figured out how to implement the function, you will feel a sense of satisfaction and accomplishment. 

So, overall, learning how to create the strcpy() function from scratch without using any library is a great way to improve your understanding of C programming, problem-solving skills, and confidence as a programmer.

Write a function that copies the string pointed to by src, including the terminating null byte (\0), to the buffer, pointed to by dest.

  • Prototype: char *_strcpy(char *dest, char *src);
  • Return value: the pointer to dest

Here’s an implementation of the strcpy() function in C, based on the provided prototype:

char *_strcpy(char *dest, char *src) {
    char *dest_orig = dest;
    while (*src != '
char *_strcpy(char *dest, char *src) {
    char *dest_orig = dest;
    while (*src != '\0') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
    return dest_orig;
}
') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '
char *_strcpy(char *dest, char *src) {
    char *dest_orig = dest;
    while (*src != '\0') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
    return dest_orig;
}
';
    return dest_orig;
}

The _strcpy() function takes two arguments: a pointer to the destination buffer dest and a pointer to the source string src.

The goal of the function is to copy the contents of the src string to the dest buffer, including the terminating null character \0.

To achieve this, the function uses a while loop that iterates over the src string character by character.

The loop continues until the null character “\0” is reached, indicating the end of the string.

During each iteration of the loop, the current character from src is copied to the current location in dest using the deference operator *. The dest and src pointers are then incremented by 1 to point to the next location in the buffer and string, respectively.

After the loop completes, the terminating null character “\0” is added to the end of the dest buffer using the assignment operator “=“.

This ensures that the copied string is null-terminated and can be correctly interpreted by other C functions.

Finally, the function returns a pointer to the start of the dest buffer. This allows the calling code to use the copied string or chain multiple function calls together.

Below is a sample program that uses the strcpy() function we just wrote:

#include <stdio.h>
char *_strcpy(char *dest, char *src);
int main() {
    char src[] = "Hello, world!";
    char dest[20];
    _strcpy(dest, src);
    printf("Source string: %s\n", src);
    printf("Copied string: %s\n", dest);
    return 0;
}

char *_strcpy(char *dest, char *src) {
    char *dest_orig = dest;
    while (*src != '
#include <stdio.h>
char *_strcpy(char *dest, char *src);
int main() {
    char src[] = "Hello, world!";
    char dest[20];
    _strcpy(dest, src);
    printf("Source string: %s\n", src);
    printf("Copied string: %s\n", dest);
    return 0;
}
char *_strcpy(char *dest, char *src) {
    char *dest_orig = dest;
    while (*src != '\0') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
    return dest_orig;
}
') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '
#include <stdio.h>
char *_strcpy(char *dest, char *src);
int main() {
    char src[] = "Hello, world!";
    char dest[20];
    _strcpy(dest, src);
    printf("Source string: %s\n", src);
    printf("Copied string: %s\n", dest);
    return 0;
}
char *_strcpy(char *dest, char *src) {
    char *dest_orig = dest;
    while (*src != '\0') {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
    return dest_orig;
}
';
    return dest_orig;
}

Output:

Source string: Hello, world!
Copied string: Hello, world!

Task to practice the C strcpy() function:

Write a program that prompts the user to enter a string and then copies the string to a buffer using strcpy() function.

Then, print the copied string back to the user.

Solution:

#include <stdio.h>

char *_copy(char *dest, char *src);

int main(void) {
    char input[20];
    char name[20];

    printf("Enter your name below ....! \n");
    fgets(input, sizeof(input), stdin);

    _copy(name, input);

    printf("Source file - %s \n", input);
    printf("Destination file - %s \n", name);

    return 0;
}

char *_copy(char *dest, char *src) {
    char *start = dest;

    while (*src != '
#include <stdio.h>
char *_copy(char *dest, char *src);
int main(void) {
char input[20];
char name[20];
printf("Enter your name below ....! \n");
fgets(input, sizeof(input), stdin);
_copy(name, input);
printf("Source file - %s \n", input);
printf("Destination file - %s \n", name);
return 0;
}
char *_copy(char *dest, char *src) {
char *start = dest;
while (*src != '\0') {
*dest++ = *src++;
}
*dest = '\0';
return start;
}

') {
        *dest++ = *src++;
    }
    
    *dest = '
#include <stdio.h>
char *_copy(char *dest, char *src);
int main(void) {
char input[20];
char name[20];
printf("Enter your name below ....! \n");
fgets(input, sizeof(input), stdin);
_copy(name, input);
printf("Source file - %s \n", input);
printf("Destination file - %s \n", name);
return 0;
}
char *_copy(char *dest, char *src) {
char *start = dest;
while (*src != '\0') {
*dest++ = *src++;
}
*dest = '\0';
return start;
}

';

    return start;
}

Output:

C strcpy()

The program starts by declaring two arrays of characters, input and name, each with a size of 20 characters. Then, it prints a message asking the user to enter their name using the printf function.

Next, the program reads in the user’s input using the fgets function, which reads a line of text from the standard input (which is usually the keyboard) and stores it in the input array.

Then, the program calls a function called _copy which takes in two arguments – a char pointer dest and a char pointer src. The _copy function then iterates over each character of the src string and copies it to the dest string. Finally, the _copy function adds a null terminator to the end of the dest string and returns the starting address of the dest string.

In the main function, the _copy function is called with the name and input arrays as arguments, which copies the user’s name from input into name. The program then prints out the original input string and the copied name string using the printf function, and finally returns 0 to indicate that the program has run successfully.

For more information on strcpy() function, check up the manual page – https://man7.org/linux/man-pages/man3/strcpy.3.html

Conclusion

The strcpy() function in C is a powerful command that allows you to copy strings in your programs.

By using the strcpy() function, you can save time and improve the efficiency of your code. In this guide, we provided step-by-step instructions on how to use the strcpy() function to create a string copy function in C.

We hope that our guide has helped you to better understand how to use this command and inspired you to start coding with confidence. So, go ahead and start creating your own string copy function today!

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