C Program to Merge Contents of Two Files into a Third File

This C Program join lines of two given files and store them in a new file.

Here is source code of the C Program to join lines of two given files and store them in a new file. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
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 * C Program to Join Lines of Two given Files and

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 * Store them in a New file
```
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 */
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#include <stdio.h>
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#include <stdlib.h>
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/* Function Prototype */
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int joinfiles(FILE *, FILE *, FILE *);
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char ch;
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int flag;
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void main(int argc, char *argv[])
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{
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    FILE *file1, *file2, *target;
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    file1 = fopen(argv[1], "r");
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    if (file1 == NULL)
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    {
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        perror("Error Occured!");
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    }
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    file2 = fopen(argv[2], "r");
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    if (file2 == NULL)
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    {
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        perror("Error Occured!");
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    }
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    target = fopen(argv[3], "a");
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    if (target == NULL)
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    {
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        perror("Error Occured!");
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    }
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    joinfiles(file1, file2, target);        /* Calling Function */

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    if (flag == 1)
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    {
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        printf("The files have been successfully concatenated\n");

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    }
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}
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```
 
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/* Code join the two given files line by line into a new file */

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int joinfiles(FILE *file1, FILE *file2, FILE *target)

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{
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    while ((fgetc(file1) != EOF) || (fgetc(file2) != EOF))

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    {
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        fseek(file1, -1, 1);
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        while ((ch = fgetc(file1)) != '\n')

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        {
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            if (ch == EOF)
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            {
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                break;
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            }
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            else
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            {
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                fputc(ch, target);
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            }
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        }
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        while ((ch = fgetc(file2)) != '\n')

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        {
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            if (ch == EOF)
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            {
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                break;
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            }
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            else
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            {
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                fputc(ch, target);
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            }
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        }
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        fputc('\n', target);
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    }
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    fclose(file1);
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    fclose(file2);
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    fclose(target);
```
```
    return flag = 1;
```
```
}
```

$ cc file7.c
$ ./a.out lines.c words.c final.c
The files have been successfully concatenated
 
/* FIRST FILE */
 
/*
Hello!!
This is a C Program File.
Consider a code to Add two numbers 
*/
 
#include <stdio.h>
/* Function Prototype */
int sum(int,  int);
void main()
{
    int num1, num2;
    printf("Enter Number1 and Number2:");
    scanf("%d %d ", num1, num2);
    sum(num1, num2);
}
 
int sum(int a, int b)
{
    return a + b;
}
 
/* SECOND FILE */
 
/*
 * this is temporary file for use in file handling
 */
#include <stdio.h>
 
int sqrt(int);
void main()
{
    int num;
    printf("enter the number:");
    scanf("%d", &num);
    sqrt(num);
    printf("The square of the given number is:", num);
}
int sqrt(int num)
{
    return num*num;
}
 
/* CONCATENATED FILE */
/*
Hello!! * this is temporary file for use in file handling
This is a C Program File. *
Consider a code to Add two numbers  */
*/
#include <stdio.h>
#include <stdio.h>
int sqrt(int);
/* Function Prototype */void main()
{
int sum(int,  int);    int num;
void main()    printf("enter the number:");
{    scanf("%d", &num);
    int num1, num2;    sqrt(num);
    printf("Enter Number1 and Number2:");    printf("The square of the given number is:", num);
    scanf("%d %d ", num1, num2);}
    sum(num1, num2);int sqrt(int num)
}{
    return num*num;
int sum(int a, int b)}
{
    return a + b;
}