CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

struct stat *sb;...lstat("...",sb); // it has not been updated since the last time it was readprintf("stated file\n");if (sb->st_mtimespec==...){print("Now updating things\n");updateThings();}

if(!access(file,W_OK)) {f = fopen(file,"w+");operate(f);...}else {
                        
                           fprintf(stderr,"Unable to open file %s.\n",file);
                     }

function readFile($filename){
                        $user = getCurrentUser();
                           
                           //resolve file if its a symbolic link
                           if(is_link($filename)){$filename = readlink($filename);}
                           if(fileowner($filename) == $user){echo file_get_contents($realFile);return;}else{echo 'Access denied';return false;}
                     }

#include <sys/types.h>
		    #include <sys/stat.h>
		    
		    ...
		    
		      struct stat sb;
		      stat("MYFILE.txt",&sb);
		      printf("file change time: %d\n",sb->st_ctime);
		      switch(sb->st_ctime % 2){
		        case 0: printf("Option 1\n"); break;
		        case 1: printf("Option 2\n"); break;
		        default: printf("this should be unreachable?\n"); break;
		      }