#include <sys/stat.h>int stat( const char *restrict pathname, struct stat *restrict buf );int fstat( int filedes, struct stat *buf );int lstat( const char *restrict pathname, struct stat *restrict buf );三個(gè)函數(shù)的返回值：若成功則返回0，若出錯(cuò)則返回-1

關(guān)于上面函數(shù)聲明中的restrict關(guān)鍵字的解釋，可參考：http://blog.csdn.net/lovekatherine/article/details/1891806（具體如下）

今天讀APUE，看到某個(gè)函數(shù)原型的聲明：

int stat (  const char * restrict  pathname,struct stat * restrict buf);

這里的restrict讓我覺得有些疑惑，一查原來(lái)是C99中增加的關(guān)鍵字那么restrict的意義是什么呢？

One of the new features in the recently apPRoved C standard C99, is the restrict pointer qualifier. This qualifier can be applied to a data pointer to indicate that, during the scope of that pointer declaration, all data accessed through it will be accessed only through that pointer but not through any other pointer. The 'restrict' keyWord thus enables the compiler to perform certain optimizations based on the premise that a given object cannot be changed through another pointer. Now you're probably asking yourself, "doesn't const already guarantee that?" No, it doesn't. The qualifier const ensures that a variable cannot be changed through a particular pointer. However, it's still possible to change the variable through a different pointer.

概括的說，關(guān)鍵字restrict只用于限定指針；該關(guān)鍵字用于告知編譯器，所有修改該指針?biāo)赶騼?nèi)容的操作全部都是基于(base on)該指針的，即不存在其它進(jìn)行修改操作的途徑；這樣的后果是幫助編譯器進(jìn)行更好的代碼優(yōu)化，生成更有效率的匯編代碼。

舉個(gè)簡(jiǎn)單的例子

int foo (int* x, int* y){*x = 0;*y = 1;return *x;}

很顯然函數(shù)foo()的返回值是0，除非參數(shù)x和y的值相同。可以想象，99％的情況下該函數(shù)都會(huì)返回0而不是1。然而編譯起必須保證生成100%正確的代碼，因此，編譯器不能將原有代碼替換成下面的更優(yōu)版本

int f (int* x, int* y){*x = 0;*y = 1;return 0;}

啊哈，現(xiàn)在我們有了restrict這個(gè)關(guān)鍵字，就可以利用它來(lái)幫助編譯器安全的進(jìn)行代碼優(yōu)化了

int f (int *restrict x, int *restrict y){*x = 0;*y = 1;return *x;}

int f (int *restrict x, int *restrict y){*x = 0;*y = 1;return 0;}

最后注意一點(diǎn)，restrict是C99中定義的關(guān)鍵字，C++目前并未引入；在GCC可通過使用參數(shù)" -std=c99"來(lái)開啟對(duì)C99的支持。

一旦給出pathname，stat函數(shù)就返回與此命名文件有關(guān)的信息結(jié)構(gòu)。fstat函數(shù)獲取已在描述符filedes上打開的有關(guān)信息。lstat函數(shù)類似于stat，但是當(dāng)命名的文件是一個(gè)符號(hào)鏈接時(shí)，lstat返回該符號(hào)鏈接的有關(guān)信息，而不是由該符號(hào)鏈接引用文件的信息。

第二個(gè)參數(shù)buf是指針，它指向一個(gè)我們必須提供的結(jié)構(gòu)。這些函數(shù)填寫由buf指向的結(jié)構(gòu)。該結(jié)構(gòu)的實(shí)際定義可能隨實(shí)現(xiàn)有所不同，但其基本形式是：

struct stat{    mode_t     st_mode;    /* file type & mode (permissions) */    ino_t      st_ino;     /* i-node number (serial number) */    dev_t      st_dev;     /* device number (file system) */    dev_t      st_rdev;    /* device number for special files */    nlink_t    st_nlink;   /* number of links */    uid_t      st_uid;     /* user ID of owner */    gid_t      st_gid;     /* group ID of owner */    off_t      st_size;    /* size in bytes, for regular files */    time_t     st_atime;   /* time of last access */    time_t     st_mtime;   /* time of last modification */    time_t     st_ctime;   /* time of last file status change */    blksize_t  st_blksize; /* best I/O block size */    blkcnt_t   st_blocks;  /* number of disk blocks allocated */};

POSIX.1未要求st_rdev、st_blksize和st_blocks字段，Single UNIX Specification XSI擴(kuò)展則定義了這些字段。

注意，該結(jié)構(gòu)中的每一個(gè)成員都是基本系統(tǒng)數(shù)據(jù)類型。

使用stat函數(shù)最多的可能是ls -l命令，用其可以獲得有關(guān)一個(gè)文件的所有信息。