FIFO - file to file transfer

 Today, we try to send a message through FIFO file from one program to another program.

(write)file_send|>>----------------file_fifo.txt----------------------->>|file_recv(read)

Sender Script

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#include<stdio.h> #include<stdlib.h> #include<string.h> #include<fcntl.h> int main() { char fil[15]="file_fifo.txt"; char wrch[20]; int siz=20; memset(wrch,'\0',siz); strcpy(wrch,"hello world"); int fd = open(fil,O_WRONLY); int cw=write(fd,wrch,siz); printf("Sender: write -%s- of %d chars to %s\n",wrch,cw,fil); return 0; }

Lets breakdown the script 

1. Line 8: Take the fifo file into a string
2. Line 10-14: Initialize the string with "hello world"
3. Line 16: Open the file in write only mode
4. Line 17: Send the text

Receiver Script

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#include<stdio.h> #include<stdlib.h> #include<fcntl.h> int main() { char fil[15]="file_fifo.txt"; mkfifo(fil,0666); char rdch[20]; int siz=20; int fd = open(fil,O_RDONLY); printf("Receiver: Waiting for message from Sender\n"); int rd=read(fd,rdch,siz); printf("Receiver: read -%s- of %d chars to %s\n",rdch,rd,fil); return 0; }

Lets breakdown the script

1. Line 8-9: Create a fifo file using mkfifo function. As receiver is to the executed before sender, we have to create fifo file here.
2. Line 11-12: Initialize character array to read the message from Sender program.
3. Line 14: Open the fifo file in read only mode
4. Line 16: Read the message from sender into rdch string

Execution

Start the receiver first.  It will be blocked waiting for message from Sender.

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# gcc fifo-recv.c -o fifo-recv # ./fifo-recv Receiver: Waiting for message from Sender

Start the sender in another terminal.  It will send the message.

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# gcc fifo-send.c -o fifo-send # ./fifo-send Sender: write -hello world- of 20 chars to file_fifo.txt

Verify in the receiver terminal, receive program would have received the message.

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# gcc fifo-recv.c -o fifo-recv # ./fifo-recv Receiver: Waiting for message from Sender Receiver: read -hello world- of 20 chars to file_fifo.txt