On Mon, Feb 20, 2023 at 09:44:41PM +1100, Darren Tucker wrote:
> $ cat test.c
> #include <stdlib.h>
> #include <stdio.h>
> int main(void)
> {
> FILE *f = fopen("testfile", "w");
> printf("fputc A=%d\n", fputc('A', f));
Is fputc() here somehow being evaluated twice? What happens
if you move the fputc() call outside the printf() call?
Or create it separately than this program.
> fclose(f);
>
> f = fopen("testfile", "a+b");
> printf("fseek=%d\n", fseek(f, -1L, SEEK_END));
> printf("c=%d\n", fgetc(f));
> printf("fputc B = %d\n", fputc('B', f));
My suggestion of course fails to explain why there's only one 'B'.
I would create the initial file separately from the test program.
I don't recall, but is there a guaranteed fflush() on open file
descriptors at program exit? Does an explicit call to fflush() do
anything?
> $ gcc test.c && ./a.out && od -x -c testfile
> fputc A=65
> fseek=0
> c=65
> fputc B = 66
> 0000000 4141 0042
> A A B
> 0000003
FWIW, this is the same output I get on both a linux and macos box.
--
nw
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