[英]N children send message to parent
What I did is I created n children and than the parent sent the message "start" to them using n pipes. 我要做的是创建了n个孩子,然后父母使用n个管道向他们发送了“开始”消息。 One pipe for each child.Now what I'm struggling to do is to send the parent back the number of each child.
每个孩子一个烟斗。现在我正在努力做的是将每个孩子的编号发回给父母。
This is my code until now: 到目前为止,这是我的代码:
int main()
{
int n=5;
int p[n-1][2];
int i;
for(i=0;i<n;i++){
if(pipe(p[i])>0){
perror("pipe error");
exit(1);
}
}
for(i=0;i<n;i++){
pid_t pid=fork();
if(pid<0){
perror("fork error");
exit(1);
}
if(pid==0){
int j;
for(j=0;j<n;j++){
close(p[j][1]);
}
for(j=0;j<i;j++){
close(p[j][0]);
}
char msg[256];
int h;
read(p[i][0],&h,sizeof(int));
read(p[i][0],msg,h*sizeof(char));
cout<<i<<"_"<<msg<<endl;
close(p[i][0]);//here I would like to send the number i to the parent
for(j=i+1;j<n;j++){
close(p[j][0]);
}
exit(0);
}
}
char ms[256];
strcpy(ms,"start");
int ho=strlen(ms);
for(i=0;i<n;i++){
if(write(p[i][1],&ho,sizeof(int))==-1){
perror("write error");
exit(1);
}
if(write(p[i][1],ms,ho*sizeof(ms))==-1){
perror("write error");
exit(1);
}
close(p[i][1]);
}
for(int j=0;j<n;j++)
close(p[j][0]);//then read the number of each child and print it
while(wait(NULL)>0){};
exit(0);
} }
And this is the output: 这是输出:
0_start
2_start
1_start
4_start
3_start
So I successfully sent the message start to each child.But I can't figure out how will the parent receive the numbers sent by the children. 这样我就成功地向每个孩子发送了开始信息,但是我不知道父母将如何接收孩子发送的电话号码。
You can do a similar process But here the parent has the read end of the pipe and the children the write end. 您可以执行类似的过程,但此处父级具有管道的读取端,子级具有写入端。 Extended the example above to include one pipe only .
将上面的示例扩展为仅包含一个管道。 You could have multiple pipes one each for each child.
您可以有多个管道,每个管道一个。
int main()
{
int n=5;
int p[n-1][2];
int pw[2]; // pipe child writes into
int i;
for(i=0;i<n;i++){
if(pipe(p[i])>0){
perror("pipe error");
exit(1);
}
}
if(pipe(pw)>0){
perror("pipe error");
exit(1);
}
for(i=0;i<n;i++){
pid_t pid=fork();
if(pid<0){
perror("fork error");
exit(1);
}
if(pid==0){
int j;
for(j=0;j<n;j++){
close(p[j][1]);
}
close(pw[0]);// close read end - child
for(j=0;j<n;j++){
if ( i!= j ) close(p[j][0]);
}
char msg[256];
int h;
read(p[i][0],&h,sizeof(int));
read(p[i][0],msg,h*sizeof(char));
cout<<i<<"_"<<msg<<endl;
close(p[i][0]);//here I would like to send the number i to the parent
write(pw[1],&i,sizeof(int)); // send i
close(pw[1]);
exit(0);
}
}
char ms[256];
strcpy(ms,"start");
int ho=strlen(ms);
int value;
for(i=0;i<n;i++){
if(write(p[i][1],&ho,sizeof(int))==-1){
perror("write error");
exit(1);
}
if(write(p[i][1],ms,ho*sizeof(ms))==-1){
perror("write error");
exit(1);
}
close(p[i][1]);
close(pw[1]); //close write end
if(read(pw[0],&value,sizeof(int))==-1){ // read from child process
perror("write error");
exit(1);
}
cout << " in main "<<value<<endl; // display number
}
for(int j=0;j<n;j++)
close(p[j][0]);//then read the number of each child and print it
while( wait(NULL) > 0 ){;}
exit(0);
}
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