unexplained behaviour

Hi all. In my searchstring() function, why does the last while() loop execute 11 times? It doesn't matter if I set TEXTLENGTH to 100,000 or 9 million, it always executes 11 times. The text file is less than 10K characters, so shouldn't the fgets return value be NULL because it has passed the end of file indicator? I want to search for the first occurrence of a string in the text file.

Thanks in advance.

Code:

// searchfilesforsting.c: search for strings in text file and replace them with another string
// 3 functions: openfile(), searchstring(), replacestring()

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

#define FILENAMELENGTH 40
#define STRINGLENGTH 1024
#define TEXTLENGTH 10000

char string[STRINGLENGTH], filename[FILENAMELENGTH], *text;
FILE *file;

void openfile(void);
void searchstring(void); // search for string in file
void replacestring(void);

int main(void)
{
    openfile();
    searchstring();


    return 0;
}

void openfile(void)
{
    do
    {
       printf("Enter file to open: ");
       fgets(filename, FILENAMELENGTH, stdin);
       filename[strlen(filename) - 1] = '\0'; // known filenames. no overflow problems
    } while((file = fopen(filename, "r"))== NULL);
}

void searchstring(void)
{
    if((text = calloc(TEXTLENGTH, sizeof(char))) == NULL) // allocate memory for reading text
    {
        puts("Memory allocation error");
        exit(EXIT_FAILURE);
    }

    do
    {
        printf("Enter string to search for: ");
    } while(fgets(string, STRINGLENGTH, stdin) == NULL);

    string[strlen(string) - 1] = '\0'; // known strings. no overflow problems

    while((fgets(text, TEXTLENGTH, file)) != NULL)
    {
        if(strstr(text, string) != NULL)
        {
            puts("A match has been found");
        }

        else
        {
            puts("A match has NOT been found");
        }
    }

    free(text);
    fclose(file);
}

Originally Posted by cfanatic

Hi all. In my searchstring() function, why does the last while() loop execute 11 times? It doesn't matter if I set TEXTLENGTH to 100,000 or 9 million, it always executes 11 times. The text file is less than 10K characters, so shouldn't the fgets return value be NULL because it has passed the end of file indicator?

How many lines has your file? 11?
fgets() stops reading after a newline or EOF (whatever comes first).

Bye, Andreas

Originally Posted by cfanatic

why does the last while() loop execute 11 times? It doesn't matter if I set TEXTLENGTH to 100,000 or 9 million..

You miss understand the meaning of fgets() second parameter. It's telling the size of the buffer. As Andreas said fgets will try to read a line of text. If it finds '\n' before the string length is buffersize - 1 then the returned string includes the '\n' plus the '\0' string terminator otherwise it stops reading but also appends '\0'.

I want to search for the first occurrence of a string in the text file.

I f you want to read the whole file into a buffer use fread().
Kurt