/* A handle for a temporary file created with write_temp_file. In
this implementation, it’s just a file descriptor. */
/*write_temp_file是个操作临时文件的句柄，本例中只是个文件描述符*/
typedef int temp_file_handle;
/* Writes LENGTH bytes from BUFFER into a temporary file. The
temporary file is immediately unlinked. Returns a handle to the
temporary file. */
/*在这函数从BUFFER中向临时文件写入LENGTH字节数据。临时文件在刚一创建就被删除掉。函数会返回临时文件的句柄。*/
temp_file_handle write_temp_file (char* buffer, size_t length)
{
/* Create the filename and file. The XXXXXX will be replaced with
characters that make the filename unique. */
/*新建文件名和文件，文件名中的XXXXXX将被随机字符串代替，以保证文件名在系统中的唯一性*/
char temp_filename[] = “/tmp/temp_file.XXXXXX”;
int fd = mkstemp (temp_filename);
/* Unlink the file immediately, so that it will be removed when the
file descriptor is closed. */
/*文件立刻被unlink，这样只要文件描述符一关闭文件就会被自动删除*/
unlink (temp_filename);
/* Write the number of bytes to the file first. */
/*首先写入即将写入数据的长度*/
write (fd, &length, sizeof (length));
/* Now write the data itself. */
/*写入数据本身*/
write (fd, buffer, length);
/* Use the file descriptor as the handle for the temporary file. */
/*函数返回文件描述符，作为临时文件的句柄*/
return fd;
}
/* Reads the contents of a temporary file TEMP_FILE created with
write_temp_file. The return value is a newly allocated buffer of
those contents, which the caller must deallocate with free.
*LENGTH is set to the size of the contents, in bytes. The
temporary file is removed. */
/*从被write_temp_file创建的临时文件中读取数据。返回值是含有文件内容的新申请到的内存块，这块内存应该又调用read_temp_file者释放。
*length是临时文件正文内容的长度。执行完read_temp_file函数后临时文件被彻底删除*/
char* read_temp_file (temp_file_handle temp_file, size_t* length)
{
char* buffer;
/* The TEMP_FILE handle is a file descriptor to the temporary file. */
/*fd是访问临时文件的文件描述符*/
int fd = temp_file;
/* Rewind to the beginning of the file. */
/*把文件指针指向文件开头*/
lseek (fd, 0, SEEK_SET);
/* Read the size of the data in the temporary file. */
/*获得临时文件正文长度*/
read (fd, length, sizeof (*length));
/* Allocate a buffer and read the data. */
/*分配内存块，读取数据*/
buffer = (char*) malloc (*length);
read (fd, buffer, *length);
/* Close the file descriptor, which will cause the temporary file to
go away. */
/*关闭文件描述符，临时文件被彻底删除*/
close (fd);
return buffer;
}
tmpfile函数
如果您使用C library I/O函数，并且并没有另一个程序使用这个临时文件（笔者注：按我的理解是在同一进程或具有父子关系的进程组中），有个更简洁的函数——tmpfile。tmpfile函数创建并打开一个临时文件，并且自动执行了unlink了这个临时文件。tmpfile函数返回一个文件描述符，如果执行失败返回NULL。当程序执行了fclose或者退出时，资源被释放。
linux系统中还提供mktemp、 tmpnam、 和tempnam等函数，但是由于健壮性和安全方面理由不建议使用他们。(T002)
