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Re: [PATCH] Open files in binary mode.

From: Eric Blake
Subject: Re: [PATCH] Open files in binary mode.
Date: Thu, 30 Jul 2020 15:33:39 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 7/30/20 3:16 PM, anonymous.maarten@gmail.com wrote:
From: Anonymous Maarten <anonymous.maarten@gmail.com>

autoconf uses binary data to filter out numerics, digits, ...
When m4, built using Visual Studio, is used as preprocessor, this fails.

With this change, there is no difference in the installed files when using m4 
built with mingw,
or m4 buit with Visual Studio.

This patch is used in the m4 recipe for conan, a c/c++ package manager.
The build script of m4 can be found at [1].

[1] https://github.com/conan-io/conan-center-index/tree/master/recipes/m4

  src/path.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/path.c b/src/path.c
index f13f3289..daaaaf65 100644
--- a/src/path.c
+++ b/src/path.c
@@ -110,7 +110,7 @@ add_include_directory (const char *dir)
  static FILE *
  m4_fopen (const char *file)
-  FILE *fp = fopen (file, "r");
+  FILE *fp = fopen (file, "rb");

Thanks for the patch. However, I'm of the opinion that installing it would be a violation of POSIX, which requires that m4 operate on text files. Since m4 can insert or remove newlines as part of macro definitions, operating in binary mode is very prone to creating incorrect line endings for a text file. Yes, the POSIX definition of a text file does NOT play nicely with Windows text files, but my interpretation of POSIX is that using "rb" instead of "r" (on platforms where it _does_ matter, since a true POSIX platform treats them identically) is only safe to do in programs where POSIX requires the utility to operate on all files, not just text files.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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