"invalid conversion from 'FILE* {aka _iobuf}' to 'int'" error

Question

I want to change size of *.txt file, which is created before. For this i use chsize. Code:

#include <iostream>
#include <stdio.h>
#include <io.h>

using namespace std;

int main()
{
    FILE *wfile; 
    wfile = fopen("test.exe", "a");
    chsize(wfile, 1024); //error is here
    file.close();
    return 0;
}

And here goes the error:

[Error] invalid conversion from 'FILE* {aka _iobuf*}' to 'int' [-fpermissive]

Q: What is wrong here? I opened the file with fopen right how it explained in the internets.

Q2: I love Windows as a OS, but I don't want to learn Windows API for C++ or something like that. Is there a option to use something portable?

`chsize()` takes an integer for the file descriptor. You can't convert a `FILE*` to that -- http://www.qnx.com/developers/docs/660/index.jsp?topic=%2Fcom.qnx.doc.neutrino.lib_ref%2Ftopic%2Fc%2Fchsize.html — David G, Aug 29 '14 at 15:32
@PiotrS. I don't know if iostream actually does everything a file API can do. I'm guessing that boost::filesystem would do everything. — IdeaHat, Aug 29 '14 at 15:41

score 3 · Accepted Answer · edited May 23 '17 at 12:34

3

First parameter for chsize is file descriptor not FILE*.

You can use function "fileno".

How can I convert a file pointer ( FILE* fp ) to a file descriptor (int fd)?

edited May 23 '17 at 12:34

Community

1
1

answered Aug 29 '14 at 15:37

Tomashu

515
1
11
20

"invalid conversion from 'FILE* {aka _iobuf}' to 'int'" error

1 Answers1