CODEWITHSUNDEEP
cfile-iosegmentation-fault
Dylan Cleaver
Dylan Cleaver

Reputation: 63

Segmentation fault in C txt file I/O

Ok guys, the purpose of my program is to read from a text file called orginal.txt containing names in the format:

Kyle Butler
Bob Jones
Nathan Moore

The program then takes these names one at a time and turns them into something like:

[email protected]

This address is then stored line by line in a new text file called final.txt

problem is, i can't get it to work, it gives me a segmentation fault and does not even get to writing to final.txt

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void write(char line[100]);

int main()
{
    FILE *fp;
    fp = fopen("original.txt", "r+");

    char line[100];
    char mod[30]="@fakeemail.com\n";
    while (fgets(line, 100, fp) != NULL){
        int i;
        for(i=0; i<100; ++i){
            if(line[i]==' '){
                line[i]='.';
            }
            if(line[i]=='\n'){
                line[i]='\0';
            }
            strcat(line, mod);
        }



        FILE *fp2;
        fp2 = fopen("final.txt", "a");

        if (fp2 != NULL){
            fputs(line, fp2);
            fclose(fp2);
        }

    }

    fclose(fp);





    return 0;
}

Upvotes: 0

Views: 3700

Answers (3)

Igor Popov
Igor Popov

Reputation: 2620

As mbratch wrote you write beyond 100 chars in line array. Here's a working code:

void write(char line[100]);

int main()
{
    FILE *fp;
    fp = fopen("original.txt", "r+");

    char line[100];
    char mod[30]="fakeemail.com\n";
    while (fgets(line, 100, fp) != NULL){
        int i;
        for(i=0; i<100; ++i){
            if(line[i]==' '){
                line[i]='.';
            }
            if(line[i]=='\n'){
                line[i]='@'; strcat(line, mod);
                line[i+strlen(mod)]='\0';
            }
        }
        FILE *fp2;
        fp2 = fopen("final.txt", "a");

        if (fp2 != NULL){
            //fputs(line, fp2); printf("%s\n",line);
            fprintf(fp2,"%s\n",line);
            fclose(fp2);
        }
    }

    fclose(fp);
    return 0;
}

Upvotes: -1

paulsm4
paulsm4

Reputation: 121599

Suggested changes:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAXLEN 100   /* Somehow parameterize "100" */

void write(char line[100]);

int main()
{
    FILE *fp;
    fp = fopen("original.txt", "r+");
    if (!fp) {   /* Check for error */
      perror ("open failed");
      return 1;
    }
    char line[MAXLEN];
     /* You don't need hard-coded array length with a static string */
    char *mod="@fakeemail.com\n"; 
    while (fgets(line, MAXLEN, fp) != NULL){
        int i;
        /* You don't need to iterate through more characters than the string contains */
        for(i=0; i<strlen(line); ++i){
            if(line[i]==' '){
                line[i]='.';
            }
            if(line[i]=='\n'){
                line[i]='\0';
            }
        }
        /* Move this OUTSIDE of your for loop */
        strcat(line, mod);

        /* Append to the output file */
        FILE *fp2;
        fp2 = fopen("final.txt", "a");
        /* You're checking for error: good! */
        if (fp2 != NULL){
            fputs(line, fp2);
            fclose(fp2);
        }

    }

    fclose(fp);
    return 0;
}

Upvotes: 0

lurker
lurker

Reputation: 58224

There are several problems with the code, but the segmentation fault is probably caused by this for loop:

for(i=0; i<100; ++i){
    if(line[i]==' '){
        line[i]='.';
    }
    if(line[i]=='\n'){
        line[i]='\0';
    }
    strcat(line, mod);
}

Every time through the loop you are concatenating mod to line. Since you iterate the loop 100 times with no other option to quit the loop, and line is only 100 characters long, very soon you will write past the 100th character of line into some other part of memory.

Upvotes: 4

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