函数练习
1.对mmap映射地址操作
mmap(), fstat()
mmap()： 将文件和设备空间映射到内存中，内存操作比磁盘更快。映射成功返回内存地址，是被返回-1.之后可以直接对映射的地址进行操作。
fstat()获取文件的状态。
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <errno.h>
int main(){
int fd=open("doc1",O_RDONLY|O_CREAT,0755);
if(fd == -1){
perror("open ");
exit(1);
}
struct stat info;
fstat(fd,&info);
/* start set NULL, means system set it. */
/* PROT_READ means memory can be read. */
/* MAP_PRIVATE means create a copy file, not influce origin file. */
void *start=mmap(NULL,info.st_size,PROT_READ,MAP_PRIVATE,fd,0);
if(start == MAP_FAILED) {
perror("mmap ");
exit(1);
}
printf("%s",(char *)start);
munmap(start,info.st_size);
close(fd);
return 0;
}
本程序将打印文件的内容。如果文件的内容为空，那么将会出现，invalid argument的错误。
2.从标准输入到标准输出
read(), write()
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(){
int n;
char buf[1000];
while((n=read(STDIN_FILENO,buf,1000))>0){
//printf("output: ");
if(write(STDOUT_FILENO,buf,n)!=n){
printf("write error\n");
}
}
if(n<0) printf("read error\n");
return 0;
}
/*
$ ./stdin_out
I sf
I sf
sd
sd
sdfsdf
sdfsdf
//output: output: output:
*/
read()函数是你输入什么，它读取什么的严格类函数。（除了ctrl+D，ctrl+C等特殊情况）
3.查看标准输入的读写属性
fcntl()
使用fcnt()查看文件的属性。
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
int main(){
int flag=fcntl(STDIN_FILENO,F_GETFL,0);
if(flag<0) {
perror("error: ");
return -1;
}
int result=flag & O_ACCMODE;
if(result == O_RDONLY){
printf("stdin read only\n");
}
else if(result == O_WRONLY){
puts("stdin write only");
}
else if(result == O_RDWR){
puts("stdin read and write");
}
else puts("stdin unknown mode");
if(flag & O_APPEND) puts("stdin append");
if(flag & O_NONBLOCK) puts("stdin nonblock");
return 0;
}
/*
./F_GETFL
stdin read and write
*/
4.终端交互，创建进程
fork(), fgets(), execlp()
使用fork()克隆一个新的进程。fork()有两个返回值，父进程中返回子进程的ID，子进程返回０。
for fgets():
出现换行字符、读到文件尾或是已读了size-1个字符才停止。最后会加上NULL作为字符串结束, 正常的返回值就是buf指针。
execlp()：从PATH 环境变量中查找文件并执行
因为终端输入的命令实则是一个小程序，需要进程资源，所以在这里需要fork新的进程
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <string.h>
int main(){
char buf[100];
pid_t pid;
int status;
printf("%% "); //out put "%"
while(fgets(buf,100,stdin)!=NULL){ // get cmd from stdin
int len=strlen(buf);
if(buf[len-1]=='\n') buf[len-1]=0;
if((pid=fork())<0) puts("fork error"); //create new process
else if(pid==0){
execlp(buf,buf,NULL); //execute buf cmd in new process
printf("could not execute %s",buf);
exit(1);
}
if(pid=waitpid(pid,&status,0)<0) puts("waitpid error");
printf("%%");
}
return 0;
}
/*
execute:
% ls
4.12.sh dex.sh doc3 for.sh t.c t
%date
Sat Aug 27 15:55:23 CST 2016
%who
root pts/1 2016-08-27 10:10 (10.21.1.109)
root pts/0 2016-08-27 09:33 (10.21.1.109)
%
*/
5.与文件的状态相关的写操作
fcntl()
在doc1文件中追加内容 “I love linux”
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
int main(){
int fd=open("doc1",O_RDWR);
int flag=fcntl(fd,F_GETFL,0);
flag|=O_APPEND;
flag=fcntl(fd,F_SETFL,&flag); // 文件的偏移量到了doc1的末尾
if(flag<0){
perror("fcntl error: ");
return -1;
}
char buff[]="I love linux";
if(write(fd,buff,sizeof(buff))<0){
perror("write error: ");
}
close(fd);
return 0;
}
6.读取文件的内容到字符串中
system(), fopen(), fgetc()
system()在使用/bin/bash如果失败则会返回127
看到fopen()可以直接使用字符串打开文件，瞬间喜欢上了它。
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
int main(){
int cmd=system("pwd > pwd_r");
if(cmd==127 || cmd==-1){
perror("system error: ");
return -1;
}
FILE *file=fopen("pwd_r","r");
if(file==NULL) {
perror("open file error: ");
return -1;
}
char buff[1005],ch;
int top=0;
while((ch=fgetc(file))!=EOF){
buff[top++]=ch;
}
buff[top]=0;
fclose(file);
printf("%s",buff);
return 0;
}
/*
$ ./fopen_write
/home/wei/mycode/test
*/
7.使用管道，父进程给子进程写一条消息“hello world.”
pipe(), fork(), read, write()
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <string.h>
int main(){
int fd[2]; // 0: read 1: write
char buff[50]="hello world";
int result=pipe(fd);
if(result==-1){
perror("create pipe error: ");
return -1;
}
pid_t pid=fork();
if(pid==-1){
perror("fork error: ");
return -1;
}
if(pid>0){ // if this is old process
result=write(fd[1],buff,strlen(buff));
printf("id: %d\n",getpid());
return 0;
}
else { // new process
read(fd[0],buff,sizeof(buff));
printf("id: %d string: %s\n",getpid(),buff);
}
return 0;
}
/*
$ ./pipe
id: 26517
id: 26518 string: hello world
*/
8.阻塞的管道
fork()
观察下面的程序：
#include <unistd.h>
#include <stdio.h>
#include <string.h>
int main(){
char buff[]="this message is sent by child process.";
int fd[2];
int result=pipe(fd);
if(result<0) {
perror("pipe error: ");
return -1;
}
pid_t pid=fork();
if(pid<0){
perror("create process error: ");
return -1;
}
else if(pid==0){
close(fd[0]);
int len=strlen(buff);
while(len>0){
int rd=write(fd[1],buff,len);
len-=rd;
if(rd<0){
perror("write error: ");
return -1;
}
else {
printf("has wrote data: %d left data: %d\n",rd,len);
}
sleep(3);
if(len==0) {
printf("write finished.\n");
}
}
}
else {
close(fd[1]);
char readbuff[105];
while(1){
int get=read(fd[0],readbuff,105);
if(get<0){
perror("read : ");
return -1;
}
else if(get==0) {
printf("here is no contents.\n");
break;
}
else {
printf("data : %s\n",readbuff);
}
}
}
return 0;
}
/*
$ ./wait_pipe
has wrote data: 38 left data: 0 #子进程写入数据
data : this message is sent by child process. #父进程读入数据
write finished. #回到了子进程
here is no contents. #这是父进程
//如果我们没有sleep(3)
has wrote data: 38 left data: 0 #子进程
write finished. #子进程
data : this message is sent by child process. #父进程
here is no contents. #父进程
*/
9.消息队列send and recv message.
ftok(), msgget(), fgets()
key_t ftok( const char * fname, int id )
fname是指定的文件名（已经存在的文件名），一般使用当前目录，如：
key_t key = ftok(“.”, 1); id是子序号。只使用8bits(1-255）。
用于保证两个不同用户下的两组相同程序获得互不干扰的IPC键值。
msgget()用于chungking或者打开消息队列。
//send.c:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/msg.h>
#include <sys/types.h>
#include <sys/ipc.h>
#define Max 105
typedef struct msgmbuf{
int msg_type;
char msg_text[Max];
}MsgBuf;
int main(){
printf("send process start: %d\n",getpid());
printf("enter your message to send, and \"end\" will kill both process.\n");
char buff[Max];
MsgBuf sendmsg;
char *msgpath="./me"; // the path of create message
key_t key=ftok(msgpath,'a');
if(key==-1) {
perror("create key error: ");
return -1;
}
int msgid=msgget(key,IPC_CREAT|0777);
if(msgid==-1){
perror("msgget error: ");
return -1;
}
while(1){
printf("please enter msg: ");
fgets(buff,Max,stdin); //file enter contents
sendmsg.msg_type=1;
strcpy(sendmsg.msg_text,buff);
if(msgsnd(msgid,(void *)&sendmsg,Max,0)){
perror("msgsnd error: ");
return -1;
}
if(strcmp(buff,"end\n")==0){
printf("send process end.\n");
return 0;
}
}
return 0;
}
//recv.c:
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/types.h>
#include <sys/msg.h>
#define Max 105
typedef struct msgmbuf{
int msg_type;
char msg_text[Max];
}MsgBuf;
int main(){
printf("recv process start: %d\n",getpid());
char buff[Max];
char *msgpath="./me";
key_t key=ftok(msgpath,'a');
int msgid=msgget(key,IPC_CREAT|0777);
if(msgid==-1){
perror("msgget error: ");
return -1;
}
MsgBuf recmsg;
while(1){
if(msgrcv(msgid,(void *)&recmsg,Max,0,0)==-1){
perror("msgrcv error: ");
return -1;
}
if(strcmp(recmsg.msg_text,"end\n")==0){
printf("recv process end.\n");
break;
}
printf("recv msg: %s",recmsg.msg_text);
}
return 0;
}
/*
$ ./send
send process start: 20436
enter your message to send, and "end" will kill both process.
please enter msg: hehe
please enter msg: I love you
please enter msg: end
send process end.
./recv
recv process start: 20437
recv msg: hehe
recv msg: I love you
recv process end.
*/
10.不同进程利用共享内存通信
shmget(), shmctl()
// myshm.h
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <string.h>
#define Size 105
// shm.c
#include "myshm.h"
int main(){
key_t key=ftok("./doc",'a');
int shmid=shmget(key,Size,IPC_CREAT|IPC_EXCL|0777);
if(shmid==-1){
puts("shmared memory exit. here is client.");
if((shmid=shmget(key,Size,0))==-1){ //the third number is 0 means we can get the exit memory id.
perror("shmget error: ");
return -1;
}
}
else puts("created new shared memory");
char buff[105], *content=NULL;
printf("If you enter \"read\", we can get contents, or \"enter\", you can input new things into shared memory.\
Other words will kill process. \n");
while(1){
printf("%% ");
if(fgets(buff,Size,stdin)<0){
perror("fgets error: ");
return -1;
}
content=(char *)shmat(shmid,0,0);
if(content == (char *)-1){
perror("shmat: ");
return -1;
}
if(strncmp(buff,"read",4)==0){
printf("data: \n%s",content);
}
else if(strncmp(buff,"enter",5)==0){
fgets(buff,Size,stdin);
strcat(content,buff);
printf("wrote it.");
}
else {
/*IPC_RMID 命令实际上不从内核删除一个段，而是仅仅把这个段标记为删除，\
* 实际的删除发生在最后一个进程离开这个共享段时。*/
shmctl(shmid,IPC_RMID,0);
printf("the process end, By.\n");
break;
}
}
return 0;
}
/*
./shm
created new shared memory
If you enter "read", we can get contents, or "enter", you can input new things into shared memory.Other words will kill process.
% enter
I love you
wrote it.% read
data:
I love you
% enter
hello world
wrote it.% s
the process end, By.
./shm
shmared memory exit. here is client.
If you enter "read", we can get contents, or "enter", you can input new things into shared memory.Other words will kill process.
% read
data:
I love you
% read
data:
I love you
hello world
% s
the process end, By.
*/
11.自定义中断信号SIGINT的处理函数
signal()
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
void stop(int sig){
printf("ctrl + c stops it!\n");
exit(0);
}
int main(){
signal(SIGINT,stop);
while(1){
puts("hello world");
}
return 0;
}
/*
./signal
hello world
hello world
hello world
hello world
hello world
hello world^Chello world
ctrl + c stops it!
*/
12.线程创建与等待
pthread_create(), pthread_join(), pthread_self()
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
void *thread_show(void *args){
int *thread_arg=(int *)args;
printf("I'm thread %lu, counter is %d\n",pthread_self(),*thread_arg); // g(long int)syscall(178),gettid() means syscall(178)
sleep(1);
}
int main(){
int i,ret;
pthread_t thread[6];
for(i=0;i<6;i++){
printf("here is thread: %d\n",i);
ret=pthread_create(&thread[i],NULL,thread_show,&i);
// 第三个参数是线程的运行函数，第四个参数是运行函数的参数
if(ret!=0) printf("error: %d,i);
}
for(i=0;i<6;i++){ //等待着线程结束，此时的i等于0
pthread_join(thread[i],NULL);
}
return 0;
}
/*
./pthread
here is thread: 0
here is thread: 1
here is thread: 2
I'm thread 140437552871168, counter is 2
I'm thread 140437544478464, counter is 2
here is thread: 3
here is thread: 4
here is thread: 5
I'm thread 140437527693056, counter is 4
I'm thread 140437519300352, counter is 5
I'm thread 140437536085760, counter is 3
I'm thread 140437510907648, counter is 0
*/
