Detecting empty file situation.

Hello:

I'm in a small bind. In my program I'm opening a file that may be empty. I can write the code around my problem of detecting whether or not a file is empty by setting my arrays to none zero values but I'd rather use a command if there is one. I checked through the tutorials and didn't find one. I know NULL is used for failing to open a file but is there a operator for a file that has no data in it? Any input will be appreciated. Thanks.

Icy

Well, a blank file should have only the EOF character. So you could use feof() to check if fp reaches end of file. Or fgetc() and check for EOF.

I don't know any ready function that does that. But it is like 1 line of code

Try something like this:

Code:

---

int main (void)
{
        FILE *fp;
        char *path = "path\\to\\file";
        long size;

        fp = fopen(path, "r");

        if (fp)
        {
                fseek (fp, 0, SEEK_END);
                size = ftell(fp);
                printf("Size of the file in bytes: %lu\n", size);
                fclose(fp);
        }

        return 0;
}

---

If size is ever 0, you know the file is empty.

Quote:

---

Originally Posted by C_ntua

Well, a blank file should have only the EOF character. So you could use feof() to check if fp reaches end of file. Or fgetc() and check for EOF.

I don't know any ready function that does that. But it is like 1 line of code

---

I've only used feof() in the form of a !feof(), I just tried it with the following code, and it didn't execute the code even though the file was empty. Any ideas?

Code:

---

    if(feof(IF))
    {
    printf("Data file is emtpy, exiting the program");
    exit(0);   
    }

---

Quote:

---

Originally Posted by xIcyx

I've only used feof() in the form of a !feof(), I just tried it with the following code, and it didn't execute the code even though the file was empty. Any ideas?

Code:

---

    if(feof(IF))
    {
    printf("Data file is emtpy, exiting the program");
    exit(0);   
    }

---

---

If you want to use the feof method, try this:

Code:

---

int main (void)
{
        FILE *fp;
        char *path = "path\\to\\file";
        long size = 0;

        fp = fopen(path, "r");

        if (fp)
        {
                while (!feof(fp))
                {
                        fgetc(fp);
                        size++;
                }
                printf("Size of the file in bytes: %lu\n", size);
                fclose(fp);
        }

        return 0;
}

---

Keep in mind though that this way, an eof char will be returned, so it will say it contains one byte.

By the way, on http://www.cplusplus.com, they have many examples of functions and your case is one of them.

Thank you for the input carrotcake.

This is what I'm leaning twoards, I was writing my first reply while you posted so did not see it first.

Code:

---

    if(IF)
    {
                fseek (IF, 0, SEEK_END);
                lSize = ftell(IF);
                if(lSize == 0)
                {
                fclose(IF);
                printf("\nInput file is empty, exting the program\n");
                system("PAUSE");
                exit(0);
    }
}

---

Edit: I fixed my problem, no clue why it didn't work before. Thanks for the help guys, and the referral to a new site for resources on C.

Are you saying that your function is pausing, and then terminating? Or are you trying to say that your function isn't pausing?

Quote:

---

Originally Posted by xIcyx

I've only used feof() in the form of a !feof(), I just tried it with the following code, and it didn't execute the code even though the file was empty. Any ideas?

Code:

---

   
if(feof(IF))
{
    printf("Data file is emtpy, exiting the program");
    exit(0);   
}

---

---

Yeah. You would need to execute first an fgetc() then the above code.

Quote:

---

Originally Posted by carrotcake1029

Are you saying that your function is pausing, and then terminating? Or are you trying to say that your function isn't pausing?

---

I fixed my problem, I honestly think it was working and because of all the password verification stuff I have getting into the program I took it as executing, just a stressed out mistake.

If handling EOF is an issue, you're probably doing it wrong.

Consider

Code:

---

int ch;
while ( (ch=fgetc(fp)) != EOF ) {
  // do stuff here
}

---

or

Code:

---

char buff[BUFSIZ];
while ( fgets( buff, sizeof buff, fp ) != NULL ) {
  // do stuff here
}

---

If the file is empty to begin with, the loops will exit without doing any "stuff"