pattern search

[_Cl0wn_]

I am having problems with this code. It compiles fine but I get the illegal operations box ONCE now instead of three times as when I started this program two days ago. The message comes after the user has entered the pattern to search for.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LENGTH 80

static int str(char *a, char *b, int len)
{
    for (;*a == *b; *a++, *b++)
    {
        if ( --len == 0)
                return 1;
    }
    return 0;
}

static char *cmp( char *string, char *word, int len)
{
    for (;*word != '\0'; *word++)
    {
        if ( str(string, word, len) == 1)
                return word;
    }
    return NULL;
}

int main(int argc, char *argv[])
{
    char *string, *word;
    int len, num,find=0;
    FILE *fd;
    
    if (argc < 2)
    {
        printf("Usage: TEXT <filename>");
        return 1;
    }
    
    if((fd=fopen(argv[1], "r"))==NULL)
    {
        printf("File Manipulation Error");
        return 1;
    }
    
    printf("Enter the search pattern: ");
    fgets( word, sizeof(word), stdin);
    num = strlen(word);
    
    while ( fgets( string, LENGTH, fd) != NULL)
    {
        if ( cmp( string, word, num) != NULL)
        {
                printf("%s found\n", word);
                ++find;
        }
    }
    
    if (find > 0)
        printf("%s found %d time(s)",word,find);
    
    return 0;
    }

P.S. I know of the strstr() function. I am doing this for learning so please don't mention that function or one that does what I am doing.

[Sargnagel]

char *string, *word;
...
fgets( word, sizeof(word), stdin);
...
while ( fgets( string, LENGTH, fd) != NULL)

string and word are just pointers to char. You did not allocate any memory to store an input string. I guess you mean something like this:

char string[LENGTH] = {'\0'}, word[LENGHT] = {'\0'};
...
fgets( word, LENGTH, stdin);
...
while ( (fgets( string, LENGTH, fd)) != NULL)

[_Cl0wn_]

Your suggestion did not work. I still get the same msgbox error when I run it.

[Prelude]

You have quite a few problems with your code, but the big one is the cmp and str functions need a signifigant rewrite:

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

#define LENGTH 80

static int str(char *a, char *b)
{
  for (;*b != '\0'; a++, b++)
  {
    if ( *b != *a)
      return 0;
  }
  return 1;
}

static char *cmp( char *string, char *word)
{
  for (;*string != '\0'; string++)
  {
    if ( str(string, word) == 1)
      return word;
  }
  return NULL;
}

int main(int argc, char *argv[])
{
  char string[LENGTH], word[LENGTH];
  int find=0;
  FILE *fd;
  
  if (argc < 2)
  {
    printf("Usage: TEXT <filename>");
    return 1;
  }
  
  if((fd=fopen(argv[1], "r"))==NULL)
  {
    printf("File Manipulation Error");
    return 1;
  }
  
  printf("Enter the search pattern: ");
  fgets( word, sizeof(word), stdin);
  if ( word[strlen ( word ) - 1] == '\n' )
    word[strlen ( word ) - 1] = '\0';
  
  while ( fgets( string, LENGTH, fd) != NULL)
  {
    if ( cmp( string, word) != NULL)
    {
      printf("%s found\n", word);
      ++find;
    }
  }
  
  if (find > 0)
    printf("%s found %d time(s)",word,find);
  
  return 0;
}

Though if given the option, I would have recoded them as such:

static int str ( const char *a, const char *b )
{
  while ( *b != '\0' ) {
    if ( *a++ != *b++ )
      return 0;
  }
  
  return 1;
}

static const char *cmp ( const char *a, const char *b )
{
  while ( *a != '\0' ) {
    if ( str ( a++, b ) == 1 )
      return b;
  }
  
  return NULL;
}

-Prelude