CODEWITHSUNDEEP
cpopen
AdrianL
AdrianL

Reputation: 335

Buffering while popen working

I'm using the following command to get a constant output of a two digit value:

pipe = popen("hcidump -a | egrep --line-buffered 'RSSI|bdaddr' | grep -A1 --line-buffered --no-group-separator 'bdaddr 78:A5:04:17:9F:66' | grep -Po --line-buffered 'RSSI:\\s+\\K.*'", "r");

I want to buffer that, so I can transform it into a integer value and work with it. but I'm not sure how to achieve that. As long as I have popen running my C-programm will not go on. I checked it with strace and he will read the value in popen and will not termit.

the rest of the code looks like that:

if (pipe) 
    {
        printf("entered pipe-if");

        while(!feof(pipe)) 
        {
            if(fgets(buffer, 128, pipe) != NULL){}
        }   
        pclose(pipe);
        printf("pclose");
        buffer[strlen(buffer)-1] = '\0';
    }

The idea behind it is that I want to use the Data to calculate a distnace in "realtime". A possibility would be that I could tell popen to end the process after x seconds, then use the buffered data and then start the process from the beginning.

Thanks for help and advice.

Upvotes: 0

Views: 576

Answers (1)

mykel
mykel

Reputation: 426

After using popen to open the pipe you should work with the file descriptor rather than the FILE pointer. You can then turn the file to non-blocking and process the data as it comes in.

int fd = fileno(pipe);
fcntl(fd, F_SETFL, O_NONBLOCK);

Then you can read data from the pipe using

bytes = read(fd, buf, bufsize);

If bytes is greater than 0, then you have some more data to process. If bytes is -1 and errno is EAGAIN, then there's nothing in the pipe. Anything else you're done. You'll have to deal with the data however it comes in (ie you don't get fgets() nicely doing things per-line)

Upvotes: 3

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