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Date: Tue, 25 Mar 2014 10:19:49 -0230
Message-ID: <CAO+Ld4uHJ6onJifw_TRrmwoFkq+0ZSjgEVEhq61XCDShCPM1Dw@mail.gmail.com>
Subject: Problem with open_memstream
From: Adam Burry <aburry AT ieee DOT org>
To: cygwin AT cygwin DOT com
Content-Type: text/plain; charset=ISO-8859-1
X-IsSubscribed: yes

I have encountered unexpected behaviour with open_memstream(). Below
is a test case that shows the problem. Shouldn't each invocation of
open_memstream() create a a stream in the same initial state?
Shouldn't 'B' be written to the beginning of the buffer?

I am running Windows 7 Professional Ver 6.1 Build 7601 Service Pack 1
on an 8 processor amd64. My cygwin DLL version is 1.7.28. I am running
the 32-bit install.


Actual output:

test: A
buf: 41 0 0 0 0 0 0 0 0 0
test: B
buf: 0 42 0 0 0 0 0 0 0 0
assertion "0 == strcmp(msg, buf)" failed: file
"test_open_memstream.c", line 33, function: Test
Aborted (core dumped)


Expected output:

test: A
buf: 41 0 0 0 0 0 0 0 0 0
test: B
buf: 42 0 0 0 0 0 0 0 0 0


Test program for GCC 4.8.2 (gcc -Wall -Wextra -pedantic -g
test_open_memstream.c):

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


FILE* RS232_1_tx = 0;


void printbuf(char* buf){
  int i = 0;
  printf("buf: ");
  for (i = 0; i < 10; ++i) {
    printf("%x ", buf[i]); }
  printf("\n"); }


void io_operations(char* msg){
  fprintf(RS232_1_tx, msg); }


void Test(char* msg) {
  char* buf = 0;
  size_t size = 0;
  printf("test: %s\n", msg);
  RS232_1_tx = open_memstream(&buf, &size);
  /* Following fseek required to work around suspected bug in the lib. */
  /* fseek(RS232_1_tx, 0, SEEK_SET); */
  assert(RS232_1_tx);
  io_operations(msg);
  fflush(RS232_1_tx);
  printbuf(buf);
  assert(0 == strcmp(msg, buf));
  fclose(RS232_1_tx);
  RS232_1_tx = 0;
  free(buf); }


int main() {
  Test("A");
  Test("B");
  return 0; }

--
Adam Burry

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