segmentaion fault with File Input/Output

This is a discussion on segmentaion fault with File Input/Output within the C Programming forums, part of the General Programming Boards category; Hi, I have a text file with the following formating: + 12 12 I am making a program that reads ...

  1. #1
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    segmentaion fault with File Input/Output

    Hi,

    I have a text file with the following formating:
    +
    12
    12

    I am making a program that reads the file and takes the file name that the user entered and conctenate the .out to the new file and output the results for example 12+12=24 so 24 should go in the new file. I am getting the segmentaion fault when I try to scan the name of the file from the user.


    My code:

    Code:
    #include<stdio.h>
    #include<stdlib.h>
    #include <string.h>
    
    int main(int argc,char**argv){
    char c[10];  /* declare a char array */
      FILE *file;  /* declare a FILE pointer  */
      char *filename;
      printf("Please enter the file name: ");
      scanf("%s",&filename);
      char *cc;
      char *dd=".txt";
      cc=strcat(filename, dd);  // the file name
       file = fopen(cc, "r");
      /* open a text file for reading */
    
      if(file==NULL) {
        printf("Error: can't open file.\n");
        return 1;
      }
      else {
        printf("File opened successfully. Contents:\n\n");
    
        while(fgets(c, 10, file)!=NULL) {
          /* keep looping until NULL pointer... */
          printf("String: %s", c);
          /* print the file one line at a time  */
        }
    
        printf("\n\nNow closing file...\n");
        fclose(file);
        return 0;
      }
    
    }

  2. #2
    ATH0 quzah's Avatar
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    Use an array instead of a pointer. filename is just a pointer, which points to nothing specific. That is to say, it's uninitialized, so it just points to some arbitrary point in memory, which likely isn't yours to play with. Use an array, or allocate some memory for your file name.


    Quzah.
    Hope is the first step on the road to disappointment.

  3. #3
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    thanks that worked I am now trying to add the 12 and the 12: It only reads the +11: its only reading the first characters.

    Code:
    #include<stdio.h>
    #include<stdlib.h>
    #include <string.h>
    
    int main(int argc,char**argv){
    char c[10];  /* declare a char array */
      FILE *file;  /* declare a FILE pointer  */
      char filename[20];
      printf("Please enter the file name: ");
      scanf("%s",&filename);
      char *cc;
      char *dd=".txt";
      cc=strcat(filename, dd);  // the file name
       file = fopen(cc, "r");
      /* open a text file for reading */
    
      if(file==NULL) {
        printf("Error: can't open file.\n");
        return 1;
      }
      else {
        printf("File opened successfully. Contents:\n\n");
        int one;
        int two;
        int three;
    
        while(fgets(c, 10, file)!=NULL) {
          one=c[0];
          two=c[1];
          three=c[2];
          printf("%s", &one);
    
        }
    
        printf("\n\nNow closing file...\n");
        fclose(file);
        return 0;
      }
    
    }
    Last edited by sara.stanley; 04-03-2006 at 10:41 PM.

  4. #4
    and the hat of wrongness Salem's Avatar
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    The edge of the known universe
    Posts
    32,659
    Code:
    $ gcc -W -Wall -ansi -pedantic -O2 foo.c
    foo.c: In function `main':
    foo.c:10: warning: char format, different type arg (arg 2)
    foo.c:11: warning: ISO C90 forbids mixed declarations and code
    foo.c:23: warning: ISO C90 forbids mixed declarations and code
    foo.c:31: warning: char format, different type arg (arg 2)
    foo.c: At top level:
    foo.c:5: warning: unused parameter 'argc'
    foo.c:5: warning: unused parameter 'argv'
    Fix your printf and scanf calls for starters.
    Also // is not a comment in standard C
    It is a comment as an extension to C89, or in C99 or C++

    > cc=strcat(filename, dd); // the file name
    > file = fopen(cc, "r");
    cc is useless, you may as well just do
    strcat(filename, dd);
    file = fopen(filename, "r");
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
    Been here, done that.
    Join Date
    May 2003
    Posts
    1,161
    1) You don't have a read to get the operator.
    2) In this code:
    Code:
        while(fgets(c, 10, file)!=NULL) {
          one=c[0];
          two=c[1];
          three=c[2];
          printf("%s", &one);
    you can't expect to move the characters into ints and expect a number out of it. After you read a number line, use atoi() to convert the buffer into a number you can do math on:
    Code:
    fgets(c, 10, file);
    one=atoi(c);
    Definition: Politics -- Latin, from
    poly meaning many and
    tics meaning blood sucking parasites
    -- Tom Smothers

  6. #6
    Registered User
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    Or use scanf() to get ints, like they were created to do.

  7. #7
    Registered User
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    Or use scanf() to get ints, like it was originally created to do.

  8. #8
    Registered User
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    thanks guys I got it to work..

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