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1. 限制
Unix系统实现定义了很多幻数和常量，这些在不同程度上依从POSIX，也遵从POSIX.1标准。这就有助于软件的可移植性。 以下两种类型的限制是必须的：
1) 编译时限制(例如，短整型的最大值是什么？)
2) 运行时限制(例如，文件名可以有多少个字符？)
编译时限制可在头文件中定义，程序在编译时可以包含头文件。但是，运行时限制则要求进程调用一个函数以获取此种限制值。
为了解决此类问题：
1) 编译时限制(例如，短整型的最大值是什么？)
2) 不与文件或目录相关联的运行时限制(sysconf函数)
3) 与文件或目录相关联的运行时限制(pathconf和fpathconf函数)
2. 函数原型
#include long sysconf(int name); long pathconf(const char *pathname, int name); long fpathname(int filedes, int name); 所有函数返回值：若成功则返回相应值；若出错则返回-1. 表1 sysconf的限制及name参数，用于标识系统限制。以__SC__开始的常量用作标识运行时限制的sysconf参数。
Name of limit
Description name argument ARG_MAX maximum length, in bytes, of arguments to the exec functions _SC_ARG_MAX ATEXIT_MAX maximum number of functions that can be registered with the atexit function _SC_ATEXIT_MAX CHILD_MAX maximum number of processes per real user ID _SC_CHILD_MAX clock ticks/second number of clock ticks per second _SC_CLK_TCK COLL_WEIGHTS_MAX maximum number of weights that can be assigned to an entry of the LC_COLLATE order keyword in the locale definition file _SC_COLL_WEIGHTS_MAX HOST_NAME_MAX maximum length of a host name as returned by gethostname _SC_HOST_NAME_MAX IOV_MAX maximum number of iovec structures that can be used with readv or writev _SC_IOV_MAX LINE_MAX maximum length of a utility's input line _SC_LINE_MAX LOGIN_NAME_MAX maximum length of a login name _SC_LOGIN_NAME_MAX NGROUPS_MAX maximum number of simultaneous supplementary process group IDs per process _SC_NGROUPS_MAX OPEN_MAX maximum number of open files per process _SC_OPEN_MAX PAGESIZE system memory page size, in bytes _SC_PAGESIZE PAGE_SIZE system memory page size, in bytes _SC_PAGE_SIZE RE_DUP_MAX number of repeated occurrences of a basic regular expression permitted by the regexec and regcomp functions when using the interval notation \{m,n\} _SC_RE_DUP_MAX STREAM_MAX maximum number of standard I/O streams per process at any given time; if defined, it must have the same value as FOPEN_MAX _SC_STREAM_MAX SYMLOOP_MAX number of symbolic links that can be traversed during pathname resolution _SC_SYMLOOP_MAX TTY_NAME_MAX length of a terminal device name, including the terminating null _SC_TTY_NAME_MAX TZNAME_MAX maximum number of bytes for the name of a time zone _SC_TZNAME_MAX 表2 sysconf的限制及name参数，用于标识系统限制。以__PC__开始的常量用作标识运行时限制的pathconf参数和fpathconf参数。
Name of limit
Description name argument FILESIZEBITS minimum number of bits needed to represent, as a signed integer value, the maximum size of a regular file allowed in the specified directory _PC_FILESIZEBITS LINK_MAX maximum value of a file's link count _PC_LINK_MAX MAX_CANON maximum number of bytes on a terminal's canonical input queue _PC_MAX_CANON MAX_INPUT number of bytes for which space is available on terminal's input queue _PC_MAX_INPUT NAME_MAX maximum number of bytes in a filename (does not include a null at end) _PC_NAME_MAX PATH_MAX maximum number of bytes in a relative pathname, including the terminating null _PC_PATH_MAX PIPE_BUF maximum number of bytes that can be written atomically to a pipe _PC_PIPE_BUF SYMLINK_MAX number of bytes in a symbolic link _PC_SYMLINK_MAX 本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/wzhwho/archive/2010/09/11/5877204.aspx |
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