linux free mem available

cat /proc/meminfo | grep MemFree | tr -s ' ' | cut -d' ' -f2
or
free -m | head -2 | tail -1 | tr -s ' ' | cut -d' '  -f4

------------------------------------------------------------------------
#include <iostream>
int check_free_ram(){
  FILE *fp;
  int status;
  char result[24];
  std::string cmd="free -m | head -2 | tail -1 | tr -s ' ' | cut -d' '  -f4";
  fp = popen(cmd.c_str(), "r");
  if (fp == NULL)
    return -1;


while (fgets(result, PATH_MAX, fp) != NULL);
    //printf("%s", result);

status = pclose(fp);
if (status == -1) {
  return -1;    
} else {
    return atoi(result);
}
---------------------------------------------------------------------------  

}