Thread: file size

hi,

how to calculate the size of a file after opening and write somthing in to file.

fp=fopen(PATH,"a+");
fprintf(fp,"%s\n","text");

after writing into file how we know memory occupied by file.

thnx in advance.

"text" == 5 bytes.

But the actual size on disk may be more, at least the block size.

What robwhit is saying is that there are "two different file-sizes". The first, and most obvious one is the number of bytes "actually in use" in the file. The second one is the number of blocks or clusters of blocks the file occupies, which may be more than the "in use" size.

By the way robwith: text is a variable, so it's not easy to determine it's length from just looking at the code.

As suggested, if you want to know how long the file is "in actual use", just use ftell (possibly combined with fseek).

Note also that you can figure out "how much fprintf() printed" by taking it's return-value - all printf type functions return a count of the number of bytes they wrote to the destination. So if you know the size (in use) of the file originally, you can calculate the new size by using the returned count from printf.

--
Mats

vart, you are indeed correct - a newline is counted as one char, even if the machine/OS definition of "newline" is CR+LF.

And I also suspect that "wide chars" printf returns a count of how many wide-chars, rather than the number of bytes printed.

--
Mats

Originally Posted by matsp

By the way robwith: text is a variable, so it's not easy to determine it's length from just looking at the code.

"text" is not a variable, it's a string constant. What scenario would it not be 5 bytes?

Originally Posted by robwhit

"text" is not a variable, it's a string constant. What scenario would it not be 5 bytes?

You are right, I read it wrong (why do people insist on using forms like "%s\n", "some constant text" - I've seen it several times --- unless there's some formatting involved, why not put it straight into the format string).

--
Mats

Originally Posted by matsp

You are right, I read it wrong (why do people insist on using forms like "%s\n", "some constant text" - I've seen it several times --- unless there's some formatting involved, why not put it straight into the format string).

Code:

fgets(buf, sizeof(buf), stdin);
printf(buf); /* uh oh */

a user could enter some formatting characters (%) and mess with the stack. So use this:

Code:

fgets(buf, sizeof(buf), stdin);
printf("%s", buf);

I guess it's just habit.

Code:

printf("%s\n", "some constant text");

does this same thing as

Code:

puts("some constant text");

though. Preference as to which one to use, I guess.

Originally Posted by robwhit

Code:

fgets(buf, sizeof(buf), stdin);
printf(buf); /* uh oh */

a user could enter some formatting characters (%) and mess with the stack. So use this:

Code:

fgets(buf, sizeof(buf), stdin);
printf("%s", buf);

I guess it's just habit.

Code:

printf("%s\n", "some constant text");

does this same thing as

Code:

puts("some constant text");

though. Preference as to which one to use, I guess.

Good point with the percent entered by user - but if it's a string literal, you'd know yourself if it's got percents or not, right?

And GCC replaces printf with no extra args with a puts as an optimization when it can ;-)

--
Mats

Originally Posted by matsp

Good point with the percent entered by user - but if it's a string literal, you'd know yourself if it's got percents or not, right?

but what if you change your code later to use variables?

Originally Posted by matsp

And GCC replaces printf with no extra args with a puts as an optimization when it can ;-)

you want your code to be portable, right?

Originally Posted by robwhit

you want your code to be portable, right?

Yes, of course - at least unless you know for sure this isn't going to move anywhere (it's no point in writing portable code when you are doing OTHER unportablt stuff).

My point about printf and puts was that:

Code:

   printf("Something to print\n");

gets converted by gcc to

Code:

   puts("something to print");

Anyways, this isn't adding anything to the original post, so lets cut it now...

--
Mats

Originally Posted by matsp

My point about printf and puts was that:

Code:

   printf("Something to print\n");

gets converted by gcc to

Code:

   puts("something to print");

oh ok, I was thinking about this:

Code:

const char *b = "Something to print\n";
printf(b);

Originally Posted by matsp

Anyways, this isn't adding anything to the original post, so lets cut it now...

agreed.