problem with fwrite

Lei Yang
2004-08-19T13:42:50Z

Hi all,

This is not really a kernel issue, apologize if anyone thinks that this
is not the right place to post it. But I am writing a kernel module and
got stuck on fwrite, really hope someone could point out what stupid
mistake I've made. I wrote a very simple code to test the idea, what I
really want to do in fred() is to read from 'dest' and write to 'src'.
It seems that upon running , fgetc doesn't get anything from in_stream,
so the first char it gets is an EOF and it breaks. Just why fwrite
didn't write anything to in_stream?

If this is not the right way to do it, what is ?

Appreciate any comments, even harsh ones.

TIA
Lei

// in test.c

#include <stdio.h>

fred(char *dest, size_t *destlen, char *src, size_t size)
{
FILE *in_stream = tmpfile();
FILE *out_stream = tmpfile();
fwrite(src, 1, size, in_stream);

int c, i;
for(i = 0;;i++)
{
c = fgetc(in_stream);
fprintf(stderr, "get char %c\n", c);
if ( c == EOF) break;
fputc(c, out_stream);
}

*destlen = i;

fseek(out_stream, 0, SEEK_SET); //rewind
fread(dest, 1, *destlen, out_stream);
fclose(in_stream);
fclose(out_stream);
fprintf(stderr, "buf = `%s', size = %d\n", dest, *destlen);
}

int main(void)
{
static char source[] = "really hope this works ";

char *bp = malloc (2048);
size_t destlen;

fred(bp, &destlen, source, strlen(source));

fprintf(stderr, "buf = `%s', size = %d\n", bp, destlen);
return 0;
}