文件IO函数

SYNOPSIS

       #include <sys/types.h>

       #include <sys/stat.h>

       #include <fcntl.h>

 

       int open(const char *pathname, int flags);

       int open(const char *pathname, int flags, mode_t mode);

 

       int creat(const char *pathname, mode_t mode);

 

 Given a pathname for a file, open() returns a file descriptor,

 

 The argument flags must include one  of  the  following  access  modes:

       O_RDONLY,  O_WRONLY,  or  O_RDWR.  These request opening the file read-

       only, write-only, or read/write, respectively.

 

  O_EXCL Ensure that this call creates the file: if this flag  is  speci‐

              fied  in  conjunction with O_CREAT, and pathname already exists,

              then open() will fail.

RETURN VALUE

       open() and creat() return the new file descriptor, or -1  if  an  error

       occurred (in which case, errno is set appropriately).

 

 

    #include <unistd.h>

 

       int close(int fd);

RETURN VALUE

       close()  returns  zero on success.  On error, -1 is returned, and errno

       is set appropriately.

 

 #include <unistd.h>

 

       ssize_t read(int fd, void *buf, size_t count);

DESCRIPTION

       read()  attempts to read up to count bytes from file descriptor fd into

       the buffer starting at buf.

 

RETURN VALUE

       On success, the number of bytes read is returned (zero indicates end of

       file), and the file position is advanced by this number.  It is not  an

       error  if  this  number  is smaller than the number of bytes requested;

       this may happen for example because fewer bytes are actually  available

       right  now  (maybe  because we were close to end-of-file, or because we

       are reading from a pipe, or from a terminal),  or  because  read()  was

       interrupted  by  a  signal.  On error, -1 is returned, and errno is set

       appropriately.  In this case it is left unspecified  whether  the  file

       position (if any) changes.

 

 

SYNOPSIS

       #include <unistd.h>

 

       ssize_t write(int fd, const void *buf, size_t count);

 

DESCRIPTION

       write()  writes  up  to  count bytes from the buffer pointed buf to the

       file referred to by the file descriptor fd.

RETURN VALUE

       On  success,  the  number  of bytes written is returned (zero indicates

       nothing was written).  On error, -1  is  returned,  and  errno  is  set

       appropriately.

 

SYNOPSIS

       #include <sys/types.h>

       #include <unistd.h>

 

       off_t lseek(int fd, off_t offset, int whence);

 

DESCRIPTION

       The lseek() function repositions the offset of the open file associated

       with the file descriptor fd to the argument  offset  according  to  the

       directive whence as follows:

 

       SEEK_SET

              The offset is set to offset bytes.

 

       SEEK_CUR

              The offset is set to its current location plus offset bytes.

 

       SEEK_END

              The offset is set to the size of the file plus offset bytes.

 

RETURN VALUE

       Upon successful completion, lseek() returns the resulting offset  loca‐

       tion  as  measured  in bytes from the beginning of the file.  On error,

       the value (off_t) -1 is returned and  errno  is  set  to  indicate  the

       error.