Merging text from two text files alternatively - c

Question

Hi I tried the same using fgets but the result are very different, I am able to achieve it through fgetc but not using fgets, what am I doing wrong. Somehow while merging a line is skipped, for instance it copies 1st file from each file and then skips to the 3rd line.
#include<stdio.h>
#include<stdlib.h>
#include<strings.h>
int main()
{
FILE *pointer1, *pointer2, *pointer3;
char source1[80],source2[80],target[80];
char str1[80],str2[80];
printf("Enter the source and source 2\n");
scanf("%s %s", source1,source2);
printf("Enter the destination\n");
scanf("%s",target);
pointer1 = fopen(source1,"r");
pointer2 = fopen(source2,"r");
pointer3 = fopen(target,"w");
if(pointer1 == NULL || pointer2==NULL || pointer3==NULL) {
printf("Cannot open a file\n ");
exit(1);
}
while(1) {
if(fgets(str1,79,pointer1)!=NULL) {
fputs(str1,pointer3);
}
if(fgets(str1,79,pointer1)==NULL)
break;
if(fgets(str2,79,pointer2)!=NULL) {
fputs(str2,pointer3);
}
if(fgets(str2,79,pointer2)==NULL)
break;
}
fclose(pointer1);
fclose(pointer2);
fclose(pointer3);
printf("Merging completed successfully\n");
printf("Press any key to exit\n");
getch();
}

Answer 1

The unexpected behaviour you are getting is actually very expected.
Even if you are, in your mind, just testing if the file is not done yet, eg: if(fgets(..) != NULL), that function actually extracts that line from a file and loses it, since you don't do anything with it.
First, I have two mentions:
At least on my computer, you need to include "conio.h" for the getch function, so I don't know how it compiles on your PC.
For future reference, please check a coding-style guide, because there are very many mistakes. Try this link: https://users.ece.cmu.edu/~eno/coding/CCodingStandard.html. For a simpler method, just search on google: "C code beautify" and they will take care of the coding style the code for you.
I'll help you with a solution here, but, to not make it too easy, I've also slipped a little mistake.
#include<stdio.h>
#include<stdlib.h>
#include<strings.h>
#include<conio.h>
int main() {
FILE *pointer1, *pointer2, *pointer3;
char source1[80], source2[80], target[80];
char str1[80], str2[80];
printf("Enter the source and source 2\n");
scanf("%s %s", source1, source2);
printf("Enter the destination\n");
scanf("%s", target);
pointer1 = fopen(source1, "r");
pointer2 = fopen(source2, "r");
pointer3 = fopen(target, "w");
if (pointer1 == NULL || pointer2 == NULL || pointer3 == NULL) {
printf("Cannot open a file\n ");
exit(1);
}
int end_first_file = 0;
int end_second_file = 0;
while (1) {
if (fgets(str1, 79, pointer1) != NULL && end_first_file == 0) {
fputs(str1, pointer3);
} else {
end_first_file = 1;
}
if (fgets(str2, 79, pointer2) != NULL && end_second_file == 0) {
fputs(str2, pointer3);
} else {
end_second_file = 1;
}
if(end_second_file && end_first_file)
break;
}
fclose(pointer1);
fclose(pointer2);
fclose(pointer3);
printf("Merging completed successfully\n");
printf("Press any key to exit\n");
getch();
}
The mistake that I've told you about, that I'm having you solve, is the following:
Taking as example:
Source1:
aa
aaa
Source2:
bb
bbb
bbbb
You will get the output:
aa
bb
aaabbb
bbbb
Q1: What happened there? "aaabbb".
Q2: How do you solve it?
Kind regards,
Claudiu