How do you split a string read from a file into arrays in C

Question

I have a simple file that has a list of 100 file names and their corresponding sizes like this:

file1.txt, 4000
file2.txt, 5000

etc.. How do I read the file line by line and then store the list of filenames into a char array and then the list of sizes into an int array? I am trying to use sscanf like this but this is not working. I am getting a seg fault:

main(){
    char line[30];
    char names[100][20];
    int sizes[100];
    FILE *fp;
    fp = fopen("filelist.txt", "rt");
    if(fp == NULL){
        printf("Cannot open filelist.txt\n");
        return;
    }

    while(fgets(line, sizeof(line), fp) != NULL){
        sscanf(line, "%s, %d", names[i][0], sizes[i]);
        printf("%d", sizes[i]);
        i++;
    }
}

possible duplicate of Reading a file line by line in C

user257111
– user257111

2012-04-29 22:06:01 +00:00
Commented Apr 29, 2012 at 22:06 — user257111
– user257111, Commented Apr 29, 2012 at 22:06
Where is i declared/initialised?

hmjd
– hmjd

2012-04-29 22:10:50 +00:00
Commented Apr 29, 2012 at 22:10 — hmjd
– hmjd, Commented Apr 29, 2012 at 22:10

hmjd · Accepted Answer · 2012-04-29 22:09:03Z

2

i is not prevented from exceeding 100, which is the maximum number of sizes and names that can be read. If there are more than one hundred lines in the file then an out of bounds access will occur. Prevent this by making this (or similar) change:

while (i < 100 & fgets(line, sizeof(line), fp) != NULL) {

answered Apr 29, 2012 at 22:09

hmjd

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1 Comment

hmjd Over a year ago

@IlanaMannine, what did you change?

Hong Wei · Accepted Answer · 2012-04-30 04:47:33Z

0

#include <stdio.h>
int main()
{
char line[30];
char names[100][20];
int sizes[100];
int i = 0;
FILE *fp;

fp = fopen("1.txt", "rt");

if(fp == NULL)
{
    printf("cannot open file\n");
    return 0;
}
while(fgets(line, sizeof(line), fp) != NULL)
{
     sscanf(line, "%[^,]", names[i]);//output the string until the char is the ","
     sscanf(line, "%*s%s", sizes);//skip the characters and get the size of the file 
        printf("%s\n", names[i]);
        printf("%s\n", sizes);

    i++;
}
fclose(fp);


return 0;
}

i think this is what you want.

you should understand the sscanf() correctly.

enter image description here

edited Apr 30, 2012 at 4:47

answered Apr 30, 2012 at 4:22

Hong Wei

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