0. 思维导图

Unix标准及实现

1. Unix标准化

1.1 ISO C

目的

提供C程序的可移植性，使其能适合于不同的操作系统

工作组

ISO/IEC JTC1/SC22/WG14

版本

ISO/C 版本

定义内容

It specifies
— the representation of C programs;
— the syntax and constraints of the C language;
— the semantic rules for interpreting C programs;
— the representation of input data to be processed by C programs;
— the representation of output data produced by C programs;
— the restrictions and limits imposed by a conforming implementation of C.

1.2 IEEE POSIX

目的

提升应用程序在各种Unix系统环境之间的可移植性

版本

• Parts before 1997
  POSIX.1: Core Services
  POSIX.1b: Real-time extensions
  POSIX.1c: Threads extensions
  POSIX.2: Shell and Utilities

• Versions after 1997
  POSIX.1-2001
  POSIX.1-2004 (with two TCs)
  POSIX.1-2008 (with one TC)

工作组

IEEE 1003.1

定义内容

• General terms, concepts, and interfaces common to all volumes of this standard, including utility conventions and C-language header definitions, are included in the Base Definitions volume.

• Definitions for system service functions and subroutines, language-specific system services for the C programming language, function issues, including portability, error handling, and error recovery, are included in the System Interfaces volume.

• Definitions for a standard source code-level interface to command interpretation services (a “shell”) and common utility programs for application programs are included in the Shell and Utilities volume.

• Extended rationale that did not fit well into the rest of the document structure, which contains historical information concerning the contents of POSIX.1-2008 and why features were included or discarded by the standard developers, is included in the Rationale (Informative) volume.

1.3 Single Unix Specification(SUS)

目的

改善应用的可移植性

X/Open系统接口(XSI)

X/Open系统接口

版本

Single Unix Specification(SUS)

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2. Unix系统实现

Unix系统实现

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3. 限制

3.1 sysconf

• 实现代码

#include "apue.h"

int main(int argc, char const *argv[])
{
    // Maximum length of a login name
    printf("LOGIN_NAME_MAX = %ld \n", sysconf(_SC_LOGIN_NAME_MAX));
    return 0;
}

• 运行结果

ckt@ubuntu:~/work/unix/code/Chapter2$ cc sysconf_test.c -o sysconf_test
ckt@ubuntu:~/work/unix/code/Chapter2$ ./sysconf_test
LOGIN_NAME_MAX = 256 

3.2 pathconf

• 实现代码

#include "apue.h"

int main(int argc, char const *argv[])
{
    printf("_PC_PATH_MAX = %ld \n", pathconf("/home/ckt/work/unix/
          code/Chapter2",_PC_PATH_MAX));
    return 0;
}

• 运行结果

ckt@ubuntu:~/work/unix/code/Chapter2$ cc pathconf_test.c -o pathconf_test
ckt@ubuntu:~/work/unix/code/Chapter2$ ./pathconf_test
_PC_PATH_MAX = 4096 

3.3 fpathconf

• 实现代码

#include "apue.h"
#include <fcntl.h>

int main(int argc, char const *argv[])
{ 
    int file_descr = -1;
    file_descr = open("/home/ckt/work/unix/code/
                         Chapter2/fpathconf_test.c", O_RDONLY);
    printf("file descriptor = %d\n", file_descr);
    printf("fpathconf = %ld \n",fpathconf(file_descr,_PC_NAME_MAX));
    return 0;
}

• 运行结果

ckt@ubuntu:~/work/unix/code/Chapter2$ ./fpathconf_test
file descriptor = 3
fpathconf = 255 

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4. 功能测试宏

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4.1 作用

4.2 示例

定义功能测试宏_TEST1和_TEST2

• 实现代码

#include "apue.h"
#include <fcntl.h>

int main(int argc, char const *argv[])
{
#if defined(_TEST1)
    printf("_TEST1\n");
#elif defined(_TEST2)
    printf("_TEST2\n");
#else
    printf("not defined\n");
#endif
    return 0;
}

• 运行结果

ckt@ubuntu:~/work/unix/code/Chapter2$ cc -D_TEST1 macros_test.c -o macros_test1
ckt@ubuntu:~/work/unix/code/Chapter2$ ./macros_test1
_TEST1

ckt@ubuntu:~/work/unix/code/Chapter2$ cc -D_TEST2 macros_test.c -o macros_test2
ckt@ubuntu:~/work/unix/code/Chapter2$ ./macros_test2
_TEST2

ckt@ubuntu:~/work/unix/code/Chapter2$ cc macros_test.c -o macros_test
ckt@ubuntu:~/work/unix/code/Chapter2$ ./macros_test
not defined

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5. 参考

• UNIX 环境高级编程 第3版
• Open Standards
• ISO/C - Approved standards
• ISO/IEC 9899:TC2
• IEEE Std 1003.1™-2008
• POSIX Versions
• The Single UNIX Specification, Version 3