I am doing programming in C++, under LINUX.
I have two independent processes. I should provide communication using named pipe.
Reader:
-creates FIFO using mkfifo – status = mkfifo(myFIFO, 0666)
-opens the pipe using open – fifo = open (myFIFO,O_RDONLY)
-reads from the pipe – num = read(fifo, temp, sizeof(temp))
Writer:
-opens pipe – fifo = open(myFIFO, O_WRONLY);
-writes to the pipe – num = write(fifo, string, strlen(string));
I have noticed that the file descriptor returned for read process
and write process are 0. Also, after command write, I can see on my terminal, the string which should be written to the pipe. I don't know why it is shown on terminal… Also, the number of bytes that are written is 0…
Would you please help me?
Thank you!!!
// read.cpp:
#define myFIFO "/temp/FIFO"
int main(){
int num, fifo, status;
char temp[32];
if (status = mkfifo(myFIFO, 0666) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (fifo = open(myFIFO, O_RDONLY) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (num= read(fifo, temp, sizeof(temp)) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
printf("In FIFO is %s \n", temp);
}
And in another file:
// write.cpp:
#define myFIFO "/temp/FIFO"
int main() {
int status, num, fifo;
char string[]="Testing...";
if (fifo = open(myFIFO, O_WRONLY) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
if (num= write(fifo, string, strlen(string)) < 0) {
printf("\n %s \n", strerror(errno));
return 0;
}
}
Best Answer
You basically have at least four errors in your code. When you create a FIFO, you have to use a file descriptor returned by "open" call. However, you are comparing it with 0 and assigning a result of a comparison to a variable that was meant to hold a file descriptor:
The correct code should look like this:
Or like this, if you insist of saving one line of code:
And exactly the same story with reading:
Correct code:
In your code that writes to FIFO there exactly the same two errors.