CODEWITHSUNDEEP
cfilegccsegmentation-fault
Ravi Yadav
Ravi Yadav

Reputation: 53

segmentation fault in files operation in C

I am trying to remove extra spaces and newlines from a file using dynaminc memory allocation but I get memory segmentation fault.

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

int main(int argc,char **argv)
{
 FILE*fp;
 char ch;
 char *p;
 int i=0,size;
 if((fp = fopen(argv[1],"r"))==NULL) 
   {
    printf("Couldnt open file\n");
    return;
   }

 fseek(fp,0,2);
 size=ftell(fp);


 p = calloc(1,size+1);
 rewind(fp);
 while((p[i] = fgetc(fp))!=EOF)
 {
   i++;
 }
 p[i]=EOF;

 fclose(fp);

 for ( i=0; p[i]!=EOF; i++)
 {
  if (p[i] == ' ' && p[i+1] == ' ')
   {
     memmove(p+i,p+i+1,strlen(p+i+1));
     i--;
   }
  if (p[i] == '\n' && p[i+1] == '\n')
   {
     memmove(p+i,p+i+1,strlen(p+i+1));
     i--;
   }
 } //all extra spaces and newlines deleted..

fp = fopen("modified","w");
if (fp==NULL)
{
 printf("coudlnt create\n");
 return;
}

i=0; 

while((fputc(p[i],fp))!=EOF)
 {
    i++;
 }
   fclose(fp);
 }

I get segmentation fault(core dumped) for the above program and if I modify the memmove instruction with strlen(p+i+2) then it doesnt give segmentation fault but gets stuck in some sort of infinite loop.Please tell me where I am going wrong.

Upvotes: 0

Views: 663

Answers (2)

Spock77
Spock77

Reputation: 3325

Do not compare char with EOF, which is int.

The whole idea with memmove is error prone, why not check bytes when you are reading it:

int b;  // should be int

while ((b = fgetc(fp)) != EOF) {
    char c = (char)b;
    if (p[i] == ' ' &&  c== ' ')  // the same for '\n'
       continue;
    p[++i] = c;
}

No need in any memmove at all.

Upvotes: 1

unwind
unwind

Reputation: 399703

Your file-reading is broken; EOF is not a character so you cannot compare a character against it and get the proper result.

Read the entire file instead, using fread(). Note that it might return a shorter length and need to be looped anyway.

Also stop using strlen(); you know the length from when you allocated the buffer and read the file in, so it's extremely wasteful in terms of performance to use strlen() all the time like you do.

Upvotes: 1

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