管道是單向的、先進先出的。它將一個程序的輸入和另一個程序的輸出連接起來。數據被一個進程讀出後,將被從管道中刪除。分爲無名和有名管道兩種。前者用於父進程和子進程間的通信,後者用於同一系統的兩個進程間通信。
二、無名管道
int pipe(int fd[2]);
其中,fd[0]用於讀管道,fd[1]用於寫管道。若成功則返回零,否則返回-1,錯誤原因存於errno中。
三、有名管道:FIFO
int mkfifo(const char* pathname,mode_t mode)
open時使用O_NONBLOCK,訪問要求無法滿足則立即出錯返回。erron是ENXIO。
例子:
- fread.c //讀文件
- #include<errno.h>
- #include<memory.h>
- #define FIFO "myfifo"
- main(){
- int fd;
- char buff[100];
- if(access(FIFO,F_OK) == -1){
- mkfifo(FIFO,0777);
- }
- fd=open(FIFO,O_RDONLY|O_NONBLOCK); //設置非阻塞打開,否則當沒有輸入時,會阻塞在read函數
- int num;
- while(1){
- memset(buff,'\0',100); //如不清空最後的字符會出現亂碼
- if((num=read(fd,buff,100))==0){
- printf("waiting.....\n");
- sleep(1);
- continue;
- }
- printf("read %d in fifo , it's %s",num,buff);
- sleep(1);
- }
- }
- fwrite.c //寫文件
- #include<stdio.h>
- #include<fcntl.h>
- #include<memory.h>
- #define FIFO "myfifo"
- main(){
- int fd;
- char buff[100];
- memset(buff,'\0',100);
- scanf("%s",buff);
- if(access(FIFO,F_OK) == -1){
- mkfifo(FIFO,0777);
- }
- fd=open(FIFO,O_WRONLY);
- int num;
- num=write(fd,buff,strlen(buff));
- printf("%d char is written! It's %s\n",num,buff);
- }
fread.c //讀文件 #include<errno.h> #include<memory.h> #define FIFO "myfifo" main(){ int fd; char buff[100]; if(access(FIFO,F_OK) == -1){ mkfifo(FIFO,0777); } fd=open(FIFO,O_RDONLY|O_NONBLOCK); //設置非阻塞打開,否則當沒有輸入時,會阻塞在read函數 int num; while(1){ memset(buff,'\0',100); //如不清空最後的字符會出現亂碼 if((num=read(fd,buff,100))==0){ printf("waiting.....\n"); sleep(1); continue; } printf("read %d in fifo , it's %s",num,buff); sleep(1); } } fwrite.c //寫文件 #include<stdio.h> #include<fcntl.h> #include<memory.h> #define FIFO "myfifo" main(){ int fd; char buff[100]; memset(buff,'\0',100); scanf("%s",buff); if(access(FIFO,F_OK) == -1){ mkfifo(FIFO,0777); } fd=open(FIFO,O_WRONLY); int num; num=write(fd,buff,strlen(buff)); printf("%d char is written! It's %s\n",num,buff); }
4、管道關閉:用close()關閉相應的文件描述符即可。