Tracking Memory Usage for Child Process

Question

I am executing a c++ program in my child process and I want to track its memory usage in the parent. Things I have tried:

1. Using SIGCHLD
2. Using waitpid

You can take a look at the commented code to get an idea of what I have tried.

int get_memory_usage(pid_t pid) { 
    int fd, data, stack; 
    char buf[4096], status_child[100000]; 
    char *vm; 
 
    sprintf(status_child, "/proc/%d/status", pid); 
    if ((fd = open(status_child, O_RDONLY)) < 0) 
        return -1; 
 
    read(fd, buf, 4095); 
    buf[4095] = '\0'; 
    close(fd); 
 
    data = stack = 0; 
 
    vm = strstr(buf, "VmData:"); 
    if (vm) { 
        sscanf(vm, "%*s %d", &data); 
    } 
    vm = strstr(buf, "VmStk:"); 
    if (vm) { 
        sscanf(vm, "%*s %d", &stack); 
    } 
 
    return data + stack;     
} 

// void handler(int sig){
//     cout<<"Sig handler caught";
// }

int main() {
    // signal(SIGCHLD,handler);
    int pid = fork();
    if(pid == -1){
        perror("fork"); 
        exit(EXIT_FAILURE); 
    }
    else if(pid == 0){
        cout<<"I am the child process"<<endl;
        const char* command = "/bin/sh";
        const char* arg1 = "sh";
        const char* arg2 = "-c";
        const char* arg3 = "/user_code/myprogram < /user_code/input.txt > /user_code/output1.txt";

        execlp(command, arg1, arg2, arg3, (char*)NULL);

        perror("execl");
        exit(EXIT_FAILURE);
    }
    else{
        cout<<"I am the parent process";

        //What am I supposed to do here?

        //child pid
        // time_t t;
        // int status;
        // pid_t childpid = pid;
        
        // do {
        //     if ((pid = waitpid(pid, &status, WNOHANG)) == -1) perror("wait() error");
        //     else if (pid == 0) {
        //         time(&t);
        //         printf("child is still running at %s", ctime(&t));
        //         cout<<"Memory used: "<<get_memory_usage(childpid)<<endl;
        //     }
        //     else {
        //         if (WIFEXITED(status)){
        //             printf("child exited with status of %d\n", WEXITSTATUS(status));
        //         }
        //         else puts("child did not exit successfully");
        //     }
        // } while (pid == 0);
    }
}

The second try using waitpid is giving me the output but I get a constant value of some 300KB. But I dont think this is the actual program usage size as I am getting the same output no matter I do any sort of memory allocation in my code.

Any help would be greatly appreciated

Things I have tried:

1. Using SIGCHLD
2. Using waitpid