UNIX环境高级编程程序1-2将标准输入复制到标准输出
// mycat/mycat.c
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#include "apue.h" #define BUFFSIZE 4096 int main() { int n; char buf[BUFFSIZE]; // By convention, all shells open three descriptors whenever a new program is run: // standard input, standard output, and standard error. // STDIN_FILENO specify the file descriptor for standard input // Unbuffered I/O is provided by the functions open, read, write, lseek, and close. // These functions all work with file descriptors. // The read function returns the number of bytes that are read, and this value is used // as the number of bytes to write. When the end of the input file is encountered, read // returns 0 and the program stops. If a read error occurs, read returns -1. while ((n = read(STDIN_FILENO, buf, BUFFSIZE)) > 0) { if (write(STDOUT_FILENO, buf, n) != n) { err_sys("write error"); } } // usually n is bigger than 0, if input ctrl + d // then n is equal to 0 if (n < 0) { err_sys("read error"); } return 0; } // The standard I/O functions provide a buffered interface to the unbuffered I/O // functions. Using standard I/O relieves us from having to choose optimal buffer sizes, // such as the BUFFSIZE constant in Figure 1.4. The standard I/O functions also simplify // dealing with lines of input (a common occurrence in UNIX applications). The fgets // function, for example, reads an entire line. The read function, in contrast, reads a // specified number of bytes. As we shall see in Section 5.4, the standard I/O library // provides functions that let us control the style of buffering used by the library. // The most common standard I/O function is printf. In programs that call // printf, we隆炉ll always include <stdio.h> normally by including apue.h as this // header contains the function prototypes for all the standard I/O functions.
makefile
mycat: mycat.c g++ -g -Wall mycat.c ../lib/libapue.a -I ../include -o mycat clean: rm mycat