How to split a text file into multiple parts in c - c

Question

What i need to do, is to take a file of n lines, and for every x lines, create a new file with the lines of the original file. An example would be this:
Original File:
stefano
angela
giuseppe
lucrezia
In this case, if x == 2, 3 file would be created, in order:
First file:
stefano
angela
Second FIle:
giuseppe
lucrezia
Third File:
lorenzo
What i've done so far is this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 10
int getlines(FILE *fp)
{
int c = 0;
int ch;
do{
ch = fgetc(fp);
if(ch == '\n')
{
c++;
}
}while(ch != EOF);
fseek(fp, 0 , SEEK_SET);
return c;
}
int ix = 0;
void Split(FILE *fp, FILE **fpo, int step, int lines, int *mem)
{
FILE **fpo2 = NULL;
char * filename = malloc(sizeof(char)*64);
char * ext = ".txt";
char number[2];
for(int i = ix; i < *mem; i++)
{
itoa(i+1, number,10);
strcpy(filename, "temp");
strcat(filename, number);
strcat(filename, ext);
if(!(fpo[i] = fopen(filename, "w")))
{
fprintf(stderr, "Error in writing\n");
exit(EXIT_FAILURE);
}
}
char ch;
int c = 0;
do{
ch = fgetc(fp);
printf("%c", ch);
if(ch == '\n')
{
c++;
}
if(c >= step)
{
c = 0;
ix++;
if(ix >= *mem && (ix*step) <= lines)
{
*mem = *mem + 1;
fpo2 = realloc(fpo, sizeof(FILE*)*(*mem));
Split(fp, fpo2, step, lines, mem);
}
}
putc(ch, fpo[ix]);
}while(ch != EOF);
}
int main()
{
FILE * fp;
if(!(fp = fopen("file.txt", "r")))
{
fprintf(stderr, "Error in opening file\n");
exit(EXIT_FAILURE);
}
int mem = N;
int lines = getlines(fp);
int step = lines/N;
FILE **fpo = malloc(sizeof(FILE *)*N);
Split(fp, fpo, step, lines, &mem);
exit(EXIT_SUCCESS);
}
I'm stack with segmentation error, i couldn't find the bug doing
gdb myprogram
run
bt
I really appreciate any help.
EDIT:
I've changed some things and now it works, but it creates an additional file that contains strange characters. I need to still adjust some things:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 10
int getlines(FILE *fp)
{
int c = 0;
int ch;
do{
ch = fgetc(fp);
if(ch == '\n')
{
c++;
}
}while(ch != EOF);
fseek(fp, 0 , SEEK_SET);
return c;
}
int ix = 0;
void Split(FILE *fp, FILE **fpo, int step, int lines, int *mem)
{
FILE **fpo2 = NULL;
char * ext = ".txt";
for(int i = ix; i < *mem; i++)
{
char * filename = malloc(sizeof(char)*64);
char * number = malloc(sizeof(char)*64);
itoa(i+1, number,10);
strcpy(filename, "temp");
strcat(filename, number);
strcat(filename, ext);
if(!(fpo[i] = fopen(filename, "w")))
{
fprintf(stderr, "Error in writing\n");
exit(EXIT_FAILURE);
}
free(number);
free(filename);
}
char ch;
int c = 0;
do{
ch = fgetc(fp);
printf("%c", ch);
if(ch == '\n')
{
c++;
}
if(c >= step)
{
c = 0;
ix++;
if(ix >= *mem && ((ix-1)*step) <= lines)
{
*mem = *mem + 1;
fpo2 = realloc(fpo, sizeof(FILE*)*(*mem));
Split(fp, fpo2, step, lines, mem);
}
}
putc(ch, fpo[ix]);
}while(ch != EOF);
}
int main()
{
FILE * fp;
if(!(fp = fopen("file.txt", "r")))
{
fprintf(stderr, "Error in opening file\n");
exit(EXIT_FAILURE);
}
int mem = N;
int lines = getlines(fp);
int step = lines/N;
FILE **fpo = malloc(sizeof(FILE *)*N);
Split(fp, fpo, step, lines, &mem);
exit(EXIT_SUCCESS);
}

Answer 1

There are a few problems in your code. But first I think you need to fix the most important thing
int step = lines/N;
Here step is 0 if your input file has less than N lines of text. This is because lines and N both are integer and integer division is rounding down.

Answer 2

I won't fix your code, but I'll help you with it. Some changes I
suggest:
Instead of getlines, use getline(3) from the standard
library.
fseek(fp, 0 , SEEK_SET) is pointless.
In char * filename = malloc(sizeof(char)*64), note that
both arguments to malloc are constant, and the size is arbitrary.
These days, it's safe to allocate filename buffers statically,
either on the stack or with static: char filename[PATH_MAX].
You'll want to use limits.h to get that constant.
Similarly you have no need to dynamically allocate your FILE
pointers.
Instead of
itoa(i+1, number,10);
strcpy(filename, "temp");
strcat(filename, number);
strcat(filename, ext);
use sprintf(filename, "temp%d%s", i+1, ext)
get familiar with err(3) and friends, for your own convenience.
Finally, your recursive Split is -- how shall we say it? -- a nightmare. Your whole program
should be something like:
open input
while getline input
if nlines % N == 0
create output filename with 1 + n/N
open output
write output
nlines++