#include <stdlib.h>
#include <stdio.h>
#include <limits.h>

int main(){
 const char *file_name = "filename";
 char abs_path_buff[PATH_MAX];

 //獲取文件路徑, 填充到abs_path_buff
 //realpath函數(shù)返回: null表示獲取失敗; 否則返回指向abs_path_buff的指針
 if(realpath(file_name, abs_path_buff)){
  printf("%s %s\n", file_name, abs_path_buff);
 }
 else{
  printf("the file '%s' is not exist\n", file_name); 
 }

 return 0;
}