How can I determine if the operating system is POSIX in C?
Solution 1
The Single UNIX Specification requires the existence of unistd.h
, which can tell you the POSIX version (via the _POSIX_VERSION
macro).
But how can you include unistd.h
if you don't know yet that you are in fact compiling on a UNIX?
That is where this GCC document comes handy. According to it, testing for the presence, or evaluation-to-true of __unix__
should tell you that the system is a UNIX. So:
#ifdef __unix__
/* Yes it is a UNIX because __unix__ is defined. */
#include <unistd.h>
/* You can find out the version with _POSIX_VERSION.
..
.. */
#endif
__unix__
is not defined on Mac OS X, so to account for that, you could instead do:
#if defined (__unix__) || (defined (__APPLE__) && defined (__MACH__))
To get a list of system specific predefined macros on your system, you may execute:
cpp -dM /dev/null
For example, my GNU/Linux system also additionally defines __linux__
and __gnu_linux__
apart from __unix__
and a bunch of other stuff.
Another useful document that you must look at is this Wiki.
It goes on to present a way of detecting the presence and version of POSIX in a way similar to the one I described above.
EDIT: Since you really want to do all this because you want to decide which directory separator to use, look at this URL. It says:
Note File I/O functions in the Windows API convert "/" to "\" as part of converting the name to an NT-style name, except when using the "\?\" prefix as detailed in the following sections.
I don't program on Windows, or know much anything about it, so I can't say I've banked on this.
Solution 2
It is possible to solve your problem using autoconf tool to discover the presence of unistd.h
and then would add a #define HAVE_UNISTD_H 1
line in a generated config.h
if unistd.h
was found, but I find that autoconf is a little hard to use, and is very out-dated.
If by any chance you are using cmake, you can solve it the same way. You could create a config.h.in
containing something like this:
#ifndef CONFIG_H
#define CONFIG_H
#cmakedefine HAVE_UNISTD_H 1
#endif
And your project's CMakeLists.txt
would look like this:
project(MyApp)
include(CheckIncludeFiles)
check_include_file("unistd.h" HAVE_UNISTD_H)
configure_file(config.h.in config.h @ONLY)
add_executable(${PROJECT_NAME} main.c)
and then to generate from the command line:
cmake . -G"Unix Makefiles"
or generate Xcode project (OSX only):
cmake . -G"Xcode"
or generate a visual studio 2013 solution project (Windows only):
cmake . -G"Visual Studio 12 2013 Win64"
cmake generators = epic win
If your operating system is POSIX, then your generated config.h
should look like this:
#ifndef CONFIG_H
#define CONFIG_H
#define HAVE_UNISTD_H 1
#endif
Otherwise, it will look like that:
#ifndef CONFIG_H
#define CONFIG_H
/* #undef HAVE_UNISTD_H */
#endif
And then you are free to your your trusted generated config.h
:
#include "config.h"
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
int main (int argc, const char * argv[])
{
#if defined(_POSIX_VERSION)
/* POSIX code here */
#else
/* non-POSIX code here */
#endif
return 0;
}
Solution 3
I know this is kind of a dead question, but I had to add this.
In C++17, there is now a __has_include
macro that can be used in #if
directives. This means that you can check for posix compliance like this:
#if __has_include(<unistd.h>)
// System is posix-compliant
#else
// System is not posix-compliant
#endif
Cheers :D!
Solution 4
Here is what I ended up with:
#include <stdio.h>
/*
NAME
basename -- return pointer to last component of a pathname
Distribution: This function is in the public domain.
Origin of function:
http://www.koders.com/c/fidEB79B7607A210C3BB7B813E793465F9D469AE912.aspx
SYNOPSIS
char *basename (const char *name)
DESCRIPTION
Given a pointer to a string containing a typical pathname
(/usr/src/cmd/ls/ls.c for example), returns a pointer to the
last component of the pathname ("ls.c" in this case).
Restrictions:
Presumes a UNIX or DOS/Windows style path with UNIX or DOS/Windows
style separators.
*/
/*
NAME:
basename:
Function:
return pointer to last component of a pathname
Distribution:
This function is in the public domain.
Origin of function:
http://www.koders.com/c/fidEB79B7607A210C3BB7B813E793465F9D469AE912.aspx
SYNOPSIS:
char *basename (const char *name)
DESCRIPTION:
Given a pointer to a string containing a typical pathname
(/usr/src/cmd/ls/ls.c for example), returns a pointer to the
last component of the pathname ("ls.c" in this case).
Restrictions:
Presumes a UNIX or DOS/Windows style path with UNIX or
DOS/Windows style separators.
Windows volumes are only a-zA-Z.
The original code suggests ISALPHA.
*/
char * basename (const char *name)
{
const char *base;
// predefined OS symbols
// http://sourceforge.net/apps/mediawiki/predef/index.php?title=Operating_Systems#UNIX_Environment
#ifndef DIR_SEPARATOR
# define DIR_SEPARATOR '/'
#endif
#ifndef DIR_SEPARATOR_2
# define DIR_SEPARATOR_2 '\\'
#endif
// Check if we are running Unix like os
// else assume Windows. Note if we guess wrong, it's not
// so bad because Windows includes the Unix separator.
#if defined (__unix__) || (defined (__APPLE__) && defined (__MACH__))
# define IS_DIR_SEPARATOR(ch) ((ch) == DIR_SEPARATOR)
#else
# define IS_DIR_SEPARATOR(ch) \
(((ch) == DIR_SEPARATOR) || ((ch) == DIR_SEPARATOR_2))
/* Skip over the disk name in MSDOS pathnames. */
if (isalpha(name[0]) && name[1] == ':')
name += 2;
#endif
for (base = name; *name; name++)
{
if (IS_DIR_SEPARATOR (*name))
{
base = name + 1;
}
}
return (char *) base;
}
int main (int argc, const char * argv[]) {
/* Return the basename of a pathname. */
#define S1 "/usr/src/cmd/ls/ls.c"
#define S2 "/usr/src/cmd/ls/abc"
#define S3 "a:/usr/src/cmd/ls/def"
#define S4 "ghi"
#define S5 "jkl.txt"
#define S6 "d:\\usr\\src\\cmd\\mno.txt"
#define S7 "d:pqm.txt"
printf(S1 " \t is %s\n",basename(S1));
printf(S2 " \t is %s\n",basename(S2));
printf(S3 " \t is %s\n",basename(S3));
printf(S4 " \t is %s\n",basename(S4));
printf(S5 " \t is %s\n",basename(S5));
printf(S6 " \t is %s\n",basename(S6));
printf(S7 " \t is %s\n",basename(S7));
return 0;
}
historystamp
I have programmed in AppleScript, Javascript, Microsoft Basic, Bash Script and Python. Mac OS Yosemite, Linux -- Fedora & Ubuntu and Windows -- XP, 7 & 10. Robert
Updated on May 21, 2021Comments
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historystamp almost 3 years
Related questions
How can I detect the operating system in C/C++?How can I find out what operating system I am running under in GCC or in ANSI C?
I'd be fine If I can know if I'm running on POSIX.
UPDATE:
It doesn't make a difference to me whether it is at compile time or run time. I'm using this in a debug routine, so performance isn't that important.
I'm looking for the path separator. Windows & Unix/Linux/BSD would be fine.
And, I'm trying to find the basename on a path. I found some solutions, but the solutions include a lot of includes which I do not want. I'm going to mod up this solution.
I'm on Mac OS X 10.4.11, and following this URL, I executed and got the following output:
mac $ touch myfile.c mac $ gcc -std=c99 -E -dM myfile.c #define __DBL_MIN_EXP__ (-1021) #define __FLT_MIN__ 1.17549435e-38F #define __CHAR_BIT__ 8 #define __WCHAR_MAX__ 2147483647 #define __DBL_DENORM_MIN__ 4.9406564584124654e-324 #define __FLT_EVAL_METHOD__ 0 #define __DBL_MIN_10_EXP__ (-307) #define __FINITE_MATH_ONLY__ 0 #define __GNUC_PATCHLEVEL__ 1 #define __SHRT_MAX__ 32767 #define __LDBL_MAX__ 1.79769313486231580793728971405301e+308L #define __APPLE_CC__ 5367 #define __UINTMAX_TYPE__ long long unsigned int #define __LDBL_MAX_EXP__ 1024 #define __SCHAR_MAX__ 127 #define __USER_LABEL_PREFIX__ _ #define __STDC_HOSTED__ 1 #define __LDBL_HAS_INFINITY__ 1 #define __DBL_DIG__ 15 #define __FLT_EPSILON__ 1.19209290e-7F #define __LDBL_MIN__ 2.00416836000897277799610805135016e-292L #define __ppc__ 1 #define __strong #define __APPLE__ 1 #define __DECIMAL_DIG__ 33 #define __LDBL_HAS_QUIET_NAN__ 1 #define __DYNAMIC__ 1 #define __GNUC__ 4 #define __DBL_MAX__ 1.7976931348623157e+308 #define __DBL_HAS_INFINITY__ 1 #define __STRICT_ANSI__ 1 #define __weak #define __DBL_MAX_EXP__ 1024 #define __LONG_LONG_MAX__ 9223372036854775807LL #define __GXX_ABI_VERSION 1002 #define __FLT_MIN_EXP__ (-125) #define __DBL_MIN__ 2.2250738585072014e-308 #define __DBL_HAS_QUIET_NAN__ 1 #define __REGISTER_PREFIX__ #define __NO_INLINE__ 1 #define _ARCH_PPC 1 #define __FLT_MANT_DIG__ 24 #define __VERSION__ "4.0.1 (Apple Computer, Inc. build 5367)" #define __BIG_ENDIAN__ 1 #define __SIZE_TYPE__ long unsigned int #define __FLT_RADIX__ 2 #define __LDBL_EPSILON__ 4.94065645841246544176568792868221e-324L #define __NATURAL_ALIGNMENT__ 1 #define __FLT_HAS_QUIET_NAN__ 1 #define __FLT_MAX_10_EXP__ 38 #define __LONG_MAX__ 2147483647L #define __FLT_HAS_INFINITY__ 1 #define __STDC_VERSION__ 199901L #define _BIG_ENDIAN 1 #define __LDBL_MANT_DIG__ 106 #define __WCHAR_TYPE__ int #define __FLT_DIG__ 6 #define __INT_MAX__ 2147483647 #define __LONG_DOUBLE_128__ 1 #define __FLT_MAX_EXP__ 128 #define __DBL_MANT_DIG__ 53 #define __WINT_TYPE__ int #define __LDBL_MIN_EXP__ (-968) #define __MACH__ 1 #define __LDBL_MAX_10_EXP__ 308 #define __DBL_EPSILON__ 2.2204460492503131e-16 #define __INTMAX_MAX__ 9223372036854775807LL #define __FLT_DENORM_MIN__ 1.40129846e-45F #define __PIC__ 1 #define __FLT_MAX__ 3.40282347e+38F #define __FLT_MIN_10_EXP__ (-37) #define __INTMAX_TYPE__ long long int #define __GNUC_MINOR__ 0 #define __DBL_MAX_10_EXP__ 308 #define __LDBL_DENORM_MIN__ 4.94065645841246544176568792868221e-324L #define __PTRDIFF_TYPE__ int #define __LDBL_MIN_10_EXP__ (-291) #define __LDBL_DIG__ 31 #define __POWERPC__ 1 mac $