convert HEX string to Decimal in arduino -

i have hex string : "0005607947" , want convert decimal number , test on this site , correctly convert decimal number , answer : "90208583" when use code wrong value ! of code wrong or did have 1 , new code problem ?

long int decimal_answer = getdec("0005607947") ;  long int getdec(string str110) {    long int id = 0 ;    int len = str110.length() ;    char buff[len] ;    int power = 0 ;     for(int = 0 ; <len ; i++) {  buff[i] = str110.charat(i); }     for(int = (len-1) ; >=0 ; i--) {        int num = buff[i] - '0' ;       id = id + num * pow(16 , power) ;       power = power + 1 ;         }     serial.println(string(id , dec));   return id ; }    // , use , error : invalid conversion 'void*'  'char**' [-fpermissive] unsigned int size = sizeof(f_value) ; char charbuf[size]; f_value.tochararray(charbuf , size);  long decimal_answer = strtol(charbuf , null , 16); serial.println(decimal_answer , dec); 

drop code, , use 'strtol' standard library.

 #include <stdlib.h>  long strtol (const char *__nptr, char **__endptr, int __base) 

for use:

long decimal_answer = strtol("0005607947", null, 16);