Thread: Hi guys, newbie here, some questions!

Originally Posted by fuso

I think for my purposes, gets() should be fine - the filename will not be longer than 99 characters.

Do I define 'filename' as a string?

And what happens if the user leans on the keyboard producing more than 99 chars?

Yes, I agree it's the users fault for leaning on the keyboard, leaving something like this

Code:

gfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff

in the filename, but it's still bad practice to use input functions that allow the application to crash with an error message when the user happens to input too much data.

And why do you believe that a filename should always be less than 99 chars? Admittedly it's unpractical, but MAX_PATH in windows is 260 chars, and in Linux somehting like 1024 chars - so if the OS can support the filename, why should your application deny it from being used in your app?

"string" is not a concept that really exists in C, as it is part of C++. None of your other code is C++.

--
Mats

You're not using it right:

fgets(filename,100, stdin);
Should be
fgets(filename,sizeof(filename), stdin);

Remember that if you lie about the buffer size to fgets, it's not better than gets.

fp=fopen(&filename[0],"r");
Is the same as
fp=fopen(filename,"r");

Also from what I can see, you're not actually doing anything with the translated characters. What are you supposed to do with them? Output to screen?

Did you even read my reply?

Well, if you declare a filename[20], then you should not use fgets(filename, 100, stdin), should you? That will allow 80 chars more than what you have space for to be read in.

I suggested that you use sizeof(filename), and that you use limits.h as an include, then use MAX_PATH to size your filename - that way you are GUARANTEED that all filenames that are allowed on that machine can fit within your fileaname, not just ones that fit in some arbitrary size that you think is big enough, be that 20, 99 or some other number.

Code:

     fp=fopen(&filename[0],"r");

is still not fixed [although it technically won't cause any problem].

I think the point I missed with fgets() is that it leaves a newline at the end of the string, so you need:

Code:

    len = strlen(filename);
    if (filename[len] == '\n') filename[len-1] = 0;
    else //  ... filename didn't fit in the variable...

--
Mats

if (filename[len] == '\n') filename[len-1] = 0;

It's wrong

len-1 should be in both places...

But I prefer

Code:

char* p = strchr(filename, '\n');
if(p) *p = '\0';

Originally Posted by vart

It's wrong

len-1 should be in both places...

But I prefer

Code:

char* p = strchr(filename, '\n');
if(p) *p = '\0';

Good spot - and strchr() and strlen() are about the same performance in the trivial implementation. strlen() can be made more optimal because we KNOW we're searching for a zero, and there are special tricks for doing that on multiword basis. But for this purpose, it's irrelevant.

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Mats

These are not tricks. Not the newline remove. It is required to open your file.
Oh and you need to use fgetc to read a character from a file.

Code:

     char* p = strchr(filename, '\n');
     if(p) *p = '\0';

This portion needs to be AFTER the input of the filename.

You may have to declare char *p up at the top of the function, and then use p =strchr(...) after the fgets(). The purpose of the above snippet is to make sure the newline that fgets() took in is removed from the string itself.

--
Mats

Make sure you actually opened the file successfully before trying to read from it; otherwise you are going to get an endless loop.
(If you can't open the file, you should probably print an error, and optionally, let the user try again.)

You may need to add "getchar()" at the end of the program to prevent the console window from closing. Try that first.