Thread: How to compare a string with a set of string that have been stored in a file

First of all, you should be checking that your file has opened successfully before trying to access it. I suspect this might be the problem - you have the extension as ".text" but I would think you mean the more typical ".txt".

Code:

scanf("%s",&m);

If 'm' is a buffer, you don't need the '&' there.

If working with strings, I recommend using "fgets()" both for user input (stdin) and reading from the file.

Finally, if you're checking many strings in the file, you would need a loop in your code - but maybe this just hasn't been implemented yet.

I would advice that you start small. You should always break down what you want to do in smaller an hopefully simpler parts.

So first off, write a program that reads your file from disk and prints every string in it. Post something along those lines first and we'll go from there.

A few hints to get you going. Check the return value from fopen(3) so you are sure that you actually could open the file. I'd advice to use fgets(3) instead of fscanf(3) to read your strings from the file. You will have to use a loop togheter with fgets to read all the strings from the file.

Originally Posted by Matticus

First of all, you should be checking that your file has opened successfully before trying to access it. I suspect this might be the problem - you have the extension as ".text" but I would think you mean the more typical ".txt".

Code:

scanf("%s",&m);

If 'm' is a buffer, you don't need the '&' there.

If working with strings, I recommend using "fgets()" both for user input (stdin) and reading from the file.

Finally, if you're checking many strings in the file, you would need a loop in your code - but maybe this just hasn't been implemented yet.

My file has .text as the extension and hence i am using that. m is a char type declared as an array to store the new string want to compare with the strings stored in the file.

Originally Posted by Jimmy

I would advice that you start small. You should always break down what you want to do in smaller an hopefully simpler parts.

So first off, write a program that reads your file from disk and prints every string in it. Post something along those lines first and we'll go from there.

A few hints to get you going. Check the return value from fopen(3) so you are sure that you actually could open the file. I'd advice to use fgets(3) instead of fscanf(3) to read your strings from the file. You will have to use a loop togheter with fgets to read all the strings from the file.

this is the code that i am using to read the strings from the file...

Code:

FILE *ptr_file;

char buf[50],m[50];
     
   ptr_file =fopen("abc.text","r");
    
    if (!ptr_file) 
       
       printf("Error opening file");
        
    else
    {

     while (fgets(buf,50, ptr_file)!=NULL)

printf("%s",buf);
}

My file has .text as the extension and hence i am using that.

Fair enough - you should still be checking that the file has successfully opened before accessing it, though.

m is a char type declared as an array to store the new string want to compare with the strings stored in the file.

Indeed - the suggestion I offered assumed this.

--------

In response to your next post - this is quite different than what you originally posted.

Try this:

- Create and post a simple, yet complete, code example that compiles (with your compare included)
- Post what is contained in a sample ".text" file
- Explain exactly what you are entering, and the result you are getting

Originally Posted by shan2014

m is a char type declared as an array to store the new string want to compare with the strings stored in the file.

So, m is some kind of buffer then. Now go and reread what Matticus posted for you.

And FYI, it is much easier to help you if you post code that is complete, so we don't have to sit around guessing what you have done. Also, make sure that the code you post compiles _without_ warnings. Also, it is usually a smart move to post an example of how your text file looks, even if we probably can make an educated guess. It makes it more likely that you will get help and that you will get help faster.

EDIT: Seeing as you are one step ahead of me Matticus, I'll leave this one to you! :-)

Originally Posted by Matticus

Fair enough - you should still be checking that the file has successfully opened before accessing it, though.



Indeed - the suggestion I offered assumed this.

--------

In response to your next post - this is quite different than what you originally posted.

Try this:

- Create and post a simple, yet complete, code example that compiles (with your compare included)
- Post what is contained in a sample ".text" file
- Explain exactly what you are entering, and the result you are getting

well here this the full code

Code:

FILE *ptr_file;

char buf[50],m[50];

   ptr_file =fopen("abc.text","r");

    if (!ptr_file) 

       printf("Error opening file");

    else
    {

     while (fgets(buf,50, ptr_file)!=NULL)

printf("%s",buf);
}
printf("\nEnter string:");
scanf("%s",&m);
    ptr_file =fopen("abc.text","r");
        fscanf(ptr_file,"%s",buf);
    
    h=strcmp(buf, m);
    
    if (h==0)
     printf("\n matched");
        else
        printf("\n Not matched");

my file 'abc' contains the following
a@b.c
d@e.f
h@i.j
So i enter various string to find if they are matched or not.

Well, that's not a complete compilable example (no includes, no "main", 'h' not declared, etc).

Anyway, first you open the file, then read the contents with "fgets()" and print in a loop. So far, so good.

Then ... you try to open the file again. That is a problem. Instead, just "rewind()" the file to start back from the beginning. You also need to restructure the code so this portion onward won't happen if the file failed to open. If the entire program hinges on the file being successfully read, then just exit on file read error (with appropriate message) - then the rest of the code doesn't have to be in an "else" block.

You still haven't fixed the "scanf()" argument I mentioned in post #2. In fact, if you used "fgets()" to read/print all lines in the file, why do you change of "fscanf()" when you start looking for the string of interest?

Also, you're not checking for the string of interest in a loop, so all you're doing is checking the first string in the file.

And you need to close the file when you're done with it.

Also never use a function to retrieve a C-string that doesn't limit the number of characters it will retrieve. The scanf() series of functions can limit the number of characters it will retrieve by using the width specifier, just don't forget to save room for the end of string character.

Code:

char C_string[100];
scanf("%99s", C_string);

Jim