Outputing top to a file from a forked process

[kardon33]

Hello Bytes,

CPU Info: Debian Lenny x86

I am trying to use the output of top to return cpu usage.
- Im am actually trying to find a simple solution to gather cpu and mem usage, I have found top is the simplest to me.

My code works great when I run it from main, however as soon as my process forks to the background when the below code runs it does not work anymore.

Any clues why it acts differently from forked vs non forked?


Thanks

    system("top -n 2 >& /var/tmp/topCpu");
    FILE *pfp;
    char line[100];
    string line2;
    string per = "";
    if ((pfp = fopen("/var/tmp/topCpu", "r")) == NULL) {
        fprintf(stderr, "POPEN Error\n");
        exit(1);
    }
    for (fgets(line, sizeof (line), pfp); fgets(line, sizeof (line), pfp);) {
        line2 = line;
        
        size_t found;
        found = line2.find("Cpu(s):");
        if(found < line2.length()){
            per = "";
            for(int i=0;i<strlen(line);i++){
                if(i >=  27 && i <= 32 && line[i] != '%'){
                    per += line[i];
                }
            }
        }
    }
    fclose(pfp);

    return atof(per.c_str());

[weaknessforcats]

I suspect you want to run your CPU usage on a separate thread rather than a separate process. That is, pthread instead of fork.

I think you are getting the CPU usage of the process but not the process with your main().

[kardon33]

No, i am not trying to get the cpu usage of any process but the entire system.

I am getting gibberish when ran from process not still active in stdin. But I cant figure out why.