Reputation: 526
How to merge the contents of two files into a new file, appearing side by side by line?
I've been trying to merge the contents of two .txt files into a third .txt file that combines the output. All I know how to do (and all I have been able to find answers for), however, is to merge them by putting the contents of the first file first, and the second file second. However, I would prefer the output to list the first line of the first file, then the first line of the second file -- followed on a new line by the second line of the first file and the second line of the second file.
To make this clearer visually, the code is currently appearing as:
file1-line1
file1-line2
file1-line3
file2-line1
file2-line2
file2-line3
... When I'd like it to appear as:
file1-line1 file2-line1
file1-line2 file2-line2
file1-line3 file2-line3
The code I have is very basic and executes the first example fine:
int main()
{
FILE *pointer1 = fopen("file1.txt", "r");
FILE *pointer2 = fopen("file2.txt", "r");
FILE *pointer3 = fopen("combined.txt", "w");
int ch;
if (pointer1 == NULL || pointer2 == NULL || pointer3 == NULL)
{
puts("Could not open files");
exit(0);
}
while ((ch = fgetc(pointer1)) != EOF)
fputc(ch, pointer3);
while ((ch = fgetc(pointer2)) != EOF)
fputc(ch, pointer3);
printf("Merged file1.txt and file2.txt into combined.txt");
fclose(pointer1);
fclose(pointer2);
fclose(pointer3);
return 0;
}
Is there a way to output the described situation? I am aware that E0F refers to the end of a file, and is likely causing an issue. Is there a similar condition for an end of a line (like E0L)?
Edit: Changed char ch to int ch.
Upvotes: 0
Views: 517
Answers (3)
Reputation: 453
#include <stdio.h>
int main()
{
FILE *pointer1 = fopen("file1.txt", "r");
FILE *pointer2 = fopen("file2.txt", "r");
FILE *pointer3 = fopen("combined.txt", "w");
char ch1, ch2;
if (pointer1 == NULL || pointer2 == NULL || pointer3 == NULL)
{
puts("Could not open files");
return 0;
}
do
{
char c1 = fgetc(pointer1);
char c2 = fgetc(pointer2);
if (feof(pointer1) || feof(pointer2))
break;
while(c1!='\n')
{
fputc(c1,pointer3);
c1=fgetc(pointer1);
if(feof(pointer1)) break;
}
fputc(' ',pointer3);
while(c2!='\n')
{
fputc(c2,pointer3);
c2=fgetc(pointer2);
if(feof(pointer2)) break;
}
fputc('\n',pointer3);
} while (1);
printf("Merged file1.txt and file2.txt into combined.txt");
fclose(pointer1);
fclose(pointer2);
fclose(pointer3);
return 0;
}
This works like you want.
Output: Combined file.txt
file1-line1 file2-line1
file1-line2 file2-line2
file1-line3 file2-line3
Upvotes: 1
Reputation: 212268
Here's one way to approach it:
#include <err.h>
#include <libgen.h>
#include <stdio.h>
#include <stdlib.h>
FILE *
xfopen(const char *path, const char *mode)
{
FILE *fp = path[0] != '-' || path[1] != '\0' ? fopen(path, mode) :
*mode == 'r' ? stdin : stdout;
if( fp == NULL ) {
perror(path);
exit(EXIT_FAILURE);
}
return fp;
}
int
main(int argc, char **argv)
{
if( argc < 3 ) {
printf("usage: %s file1 file2\n", basename(argv[0]));
}
FILE *pointer1 = xfopen(argv[1], "r");
FILE *pointer2 = xfopen(argv[2], "r");
FILE *current = pointer1;
int ch;
while( ( ch = fgetc(current)) != EOF ) {
if( ch == '\n' ) {
if( current == pointer1 ) {
int k;
current = pointer2;
if( (k = fgetc(current)) != EOF ) {
ungetc(k, current);
ch = ' ';
}
} else {
current = pointer1;
}
}
putchar(ch);
}
if( ferror(current) ) {
err(EXIT_FAILURE, "Error reading %s",
current == pointer1 ? argv[1] : argv[2]);
}
current = current == pointer1 ? pointer2 : pointer1;
while( (ch = fgetc(current)) != EOF) {
putchar(ch);
}
fclose(pointer1);
fclose(pointer2);
return 0;
}
Upvotes: 1
Reputation: 148965
First, if you have a Unix-like system, the paste command already does that. Next as you want to process lines, you should use fgets. Here you have to loop over input files one line at a time, copy the lines to the output file without the newline, and add the new line after copying everything.
As the processing for both input files is the same, and as I am lazy, I wrote a function to only write it once. In the end code could be:
FILE *copyline(FILE *in, FILE *out) {
char line[256];
if (in != NULL) {
for (;;) { // loop if the line is larger that sizeof(line)
if (NULL == fgets(line, sizeof(line), in)) { // EOF on file1
fclose(in);
in = NULL;
break;
}
size_t end = strcspn(line, "\n");
if (end != 0) fwrite(line, 1, end, out); // smth to write
if (end != strlen(line)) break; // \n found: exit loop
}
}
return in;
}
int main()
{
FILE *pointer1 = fopen("file1.txt", "r");
FILE *pointer2 = fopen("file2.txt", "r");
FILE *pointer3 = fopen("combined.txt", "w");
const char sep[] = " "; // a separator between lines of both file
if (pointer1 == NULL || pointer2 == NULL || pointer3 == NULL)
{
puts("Could not open files");
exit(0);
}
for (;;) {
pointer1 = copyline(pointer1, pointer3);
fwrite(sep, strlen(sep), 1, pointer3);
pointer2 = copyline(pointer2, pointer3);
if (pointer1 == NULL && pointer2 == NULL) break;
fputc('\n', pointer3); // if smth was written, add a newline
printf(".");
}
printf("Merged file1.txt and file2.txt into combined.txt");
fclose(pointer3);
return 0;
}
Upvotes: 1
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