Hex String to Decimal Conversion

[paul51]

I have a Hex value in a string that I need to convert to decimal. Does anyone know how to do this?

 

[xwb]

Try strtol or strtoul

The first parameter is the string to be converted.
The second is a pointer to a char*. It points to the character after the last character converted. If you're not using it then just put in a dummy variable.
The third parameter is the base, which, in your case, will be 16.

 

[drewdaman]

http://www.daniweb.com/techtalkforums/thread10227.html

 

[drewdaman]

or if you want to do it by hand, the alogorithm is very simple! (sounds like homework so you might not be able to use predefined functions )

have some sort of enumeration that holds teh value (dec) of each hex char (0-F)...

loop through starting at the right of the string

int a;
int total=0
int j=0
int i=strlen hex
while i>0
a=get value of char at i from enum
total=total+(16^j * a)
i--; j++;


i'm assuming unsigned here.

 

[xwb]

Just to clarify, in drewdaman's pseudo code, "16^j" means "16 to the power of j" not "16 xor j"

^ means "exclusive or" in C/C++
^ means pointer in Pascal
^ means "to the power of" in some languages (the last one I used that had this notation was Algol 68!)

 

[uolj]

You could also use a stringstream.

 

[drewdaman]

yeah "^" means to the power! you will have to use the pow function from the math library. what i posted was just an algorithm... with some short hand!

 

[ArkM]

Oh, never use pow() function in that case! Better use a simple shift (<<4 for accumulated result).
get value of char at i from enum - sound mysterious and ambiguous...

 

[Polu]

Algol 68 !!!

How old are you, xwb?

 

[drewdaman]

whats wrong with the pow() function ArkM?

 

[drewdaman]

ps. as for the enumeration... i don't really remember the syntax for it.. but if you have an enum

hexdigits={0,1,2,3,4,5,6,7,8,9,10,A,B,C,D,E,F}

there must be a way to figure out the position a certain character is at in the enumeration...

i know you can do:
days={sun, mon, tues, .., etc}
and sun=1, mon=2 etc.
maybe the reverse is possible? i haven't used enums in a long time.. so i can't remember... but the point was that you should map the hex digit to a decimal digit some how. the enum was just a suggestion...

 

[ArkM]

The pow() function is too expensive: floating point calculations with exp and log (). We have integral type data and powers of 16 in the case above.
So using pow() == nuclear strike against a petty thief.

 

[drewdaman]

hehe.. ok. point taken

 

[xwb]

Polu - how old? Make a guess. Cut my teeth on Algol 60 on an ICL 1904S in 1975.

 

[tmiketx]

a homebrew fragile algorithm that half-works is simple (obviously! haha) but the CORRECT algorithm that works across character sets is in the library functions strtol() and strtoul().