How do I get the size of a file I opened in C?

Question

I have opened a file (with fopen() ), so, normally, I have a pointer to a file structure. The problem is, I need to know the size of the file I opened. I thought it might be somwere in the structure, the file descriptor, perhaps. But, I have no idea what FILE structure looks like, or what members it has. So, what would be the easiest way for me to find out the size of the file I just opened?

I'm writting in C.
Thank you in advance.

Answer 1

There is a function to return the file length.

Under Turbo C++ (DOS version) and Borland C++

filelength(fileno(ifp));

Visual C++

_filelength(fileno(fp));

Recommend that fp is in Binary Mode

Answer 2

Hi there!



The system call to use is fstat().



fstat takes two parameters: a pointer to a file structure, and a "stat" structure. You create the "stat" struct, and pass that into fstat too. Then fstat fills it out. Your file size is in "st_size" in the structure.



If you're using Mac OS X or Linux (or another such OS), you can enter "man fstat" at the command line to learn more. Or check your programming documentation. Or check the link I've posted below.



I could give you some code, but I think that should be enough to go on with. Good luck!



Edit: Ugh, sorry, I'm silly. fstat takes a "file descriptor". You turn a "FILE *" into a file descriptor with the fileno() call. Make your call: fstat(fileno(file_in), &FileInfo)

Answer 3

I don't think there is a function to determine the size of a file.

What u can do is, when u have the FILE struct is to get the end position of the last character, which is also the file size!



long lSize;

FILE * pFile;



// open the file

pFile =fopen("somefilename.ext", "r");



fseek (pFile , 0 , SEEK_END); // move the read pointer to end of the file

lSize = ftell (pFile); // get the file position == file size

rewind (pFile); // move back to the front of the file





U might get in trouble if ur file is extremely large.

Then the function ftell will produce the wrong value. (compiler depend)

Maybe u can use

int fgetpos ( FILE * stream, fpos_t * position );

Answer 4

// open the file

FILE * pFile = fopen("c:\\temp\\test2.txt", "rb");



// seek to the end

fseek(pFile, 0, SEEK_END);



// the current file position tells us how big this file is

int fileSize = ftell(pFile);



// seek back to the beginning so we can start reading it in

fseek(pFile, 0, SEEK_SET);



Calroth's answer of using fstat is correct when using handles returned by open()/close(), but I don't think it works with FILE *.

Answer 5

properly the 1st difficulty i see is which you need to contain the completed root direction of the record you % opened. ex: F:gradesfoldergrades.txt and im fairly beneficial you need to outline the marks. a C++ application wont check out a wall of text fabric and %. out the grades. you need to enter them into it as set values.