fopen deprecated warning

Question

On Visual Studio 2005 C   compiler  I get the following warning when my code uses the fopen and such calls   1 gt foo cpp 5    warning C4996   fopen  was declared deprecated 1 gt         c  program files microsoft visual studio 8 vc include stdio h 234    see declaration of  fopen  1 gt         Message   This function or variable may be unsafe  Consider using fopen s instead  To disable deprecation  use  CRT SECURE NO DEPRECATE  See online help for details     How do I prevent this

User · Answer

I also got the same problem  When I try to add the opencv library   include  lt opencv cv h gt    I got not a warning but an error   error C4996   fopen   This function or variable may be unsafe  Consider using fopen s instead  To disable deprecation  use  CRT SECURE NO WARNINGS  See online help for details     c  program files  x86  opencv build include opencv2 flann logger h     I also used the preprocessor directives as mentioned  But that didn t solve the problem   I solved it by doing as follows    Go to Properties -  C C   -  Precompiled Headers -  Choose Not Using Precompiled Headers in Precompiled Header

User · Answer

It looks like Microsoft has deprecated lots of calls which use buffers to improve code security  However  the solutions they re providing aren t portable  Anyway  if you aren t interested in using the secure version of their calls  like fopen s   you need to place a definition of  CRT SECURE NO DEPRECATE before your included header files  For example    define  CRT SECURE NO DEPRECATE  include  lt stdio h gt    The preprocessor directive can also be added to your project settings to effect it on all the files under the project  To do this add  CRT SECURE NO DEPRECATE to Project Properties -  Configuration Properties -  C C   -  Preprocessor -  Preprocessor Definitions

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If you code is intended for a different OS  like Mac nbsp OS nbsp X  Linux  you may use following    ifdef  WIN32  define  CRT SECURE NO DEPRECATE  endif

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I am using VisualStdio 2008  In this case I often set Preprocessor Definitions     Menu   Project    ProjectName  Properties    Alt F7   If click this menu or press Alt   F7 in project window  you can see  Property Pages  window   Then see menu on left of window      Configuration Properties   C C     Preprocessor   Then add  CRT SECURE NO WARNINGS to   Preprocessor Definitions

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For those who are using Visual Studio 2017 version  it seems like the preprocessor definition required to run unsafe operations has changed  Use instead    define  CRT SECURE NO WARNINGS   It will compile then

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Many of Microsoft s secure functions  including fopen s    are part of C11  so they should be portable now  You should realize that the secure functions differ in exception behaviors and sometimes in return values  Additionally you need to be aware that while these functions are standardized  it s an optional part of the standard  Annex K  that at least glibc  default on Linux  and FreeBSD s libc don t implement   However  I fought this problem for a few years  I posted a larger set of conversion macros here   For your immediate problem  put the following code in an include file  and include it in your source code    pragma once  if  defined FCN S MACROS H      define   FCN S MACROS H      include  lt cstdio gt      include  lt string gt     Need this for  stricmp    using namespace std          MSC VER   1400 is MSVC 2005   MSC VER   1600  MSVC 2010  was the current       value when I wrote  some of  these macros       if  defined  MSC VER   amp  amp    MSC VER  gt   1400           inline extern       FILE    fcnSMacro fopen s char  fname  char  mode           FILE  fptr           fopen s  amp fptr  fname  mode            return fptr                 define fopen fname  mode             fcnSMacro fopen s  fname    mode        else        define fopen s fp  fmt  mode           fp  fopen   fmt    mode        endif    MSC VER   endif    FCN S MACROS H   Of course this approach does not implement the expected exception behavior

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This is just Microsoft being cheeky   Deprecated  implies a language feature that may not be provided in future versions of the standard language   standard libraries  as decreed by the standards committee  It does not  or should not mean   we  unilaterally  don t think you should use it   no matter how well-founded that advice is

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Consider using a portability library like glib or the apache portable runtime  These usually provide safe  portable alternatives to calls like these  It s a good thing too  because these insecure calls are deprecated in most modern environments

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If you want it to be used on many platforms  you could as commented use defines like    if defined  MSC VER     defined WIN32      defined  WIN32     defined   WIN32                                 defined WIN64        defined  WIN64     defined   WIN64              errno t err   fopen s  amp stream name   w      endif   if defined unix            defined   unix          defined   unix                                 defined linux           defined   linux         defined   linux                                 defined sun             defined   sun                               defined BSD             defined   OpenBSD       defined   NetBSD                                 defined   FreeBSD       defined   DragonFly                                defined sgi             defined   sgi                               defined   MACOSX        defined   APPLE                                 defined   CYGWIN              stream   fopen name   w      endif

User · Answer

Well you could add a    pragma warning  disable   4996    before you use fopen  but have you considered using fopen s as the warning suggests  It returns an error code allowing you to check the result of the function call    The problem with just disabling deprecated function warnings is that Microsoft may remove the function in question in a later version of the CRT  breaking your code  as stated below in the comments  this won t happen in this instance with fopen because it s part of the C  amp  C   ISO standards

[visual-c++] fopen deprecated warning

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