#include <stdlib.h>

 #include <stdio.h>

 #include <limits.h>

 int main(){

     const char *file_name = "filename";

     char abs_path_buff[PATH_MAX];

     //获取文件路径, 填充到abs_path_buff

     //realpath函数返回: null表示获取失败; 否则返回指向abs_path_buff的指针

     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 ;

 }