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hello everyone,
i'm trying to iterate through a hexadecimal number, which is held in a string. i was hoping to find a neater way to do this than with mechanically diong it unit by unit. is there any easier way to treat hex numbers / iterate through them incrementing with each iteration?
sorry if this is a stupid question, but it seems that if you can format out put as hex numbers there should be an easier way to increment them.
thanks for all and any replies.
I guess the question is "why are you holding hex numbers in a string?"
Does your hexadecimal number string begin with '0x' or '0X'? If so, you can use the strtoi function to convert it to an integer. Then you can increment the integer, and use sprintf to print the incremented integer back to a string.
That should be an l (ell) not an i (eye).Quote:
Originally Posted by TheBigH
strto*:
d = double
f = float
ld = long double
l = long
ll = long long
ul = unsigned long
ull = unsigned long long
imax - convert strings to maximum sized integers
uimax - "
Quzah.
hey folkes,
thanks for your quick replies. i guess i could use an integer, or add '0x' to the beggining of the string or something like that. basically it is passed into the function, and then to another function as a char* without a '0x' at the beginning. i guess i can turn it into an int and back, and then chop of the '0x'. i guess i'm surprised that there isn't a way to use it as it is.
Probably because it is completely ludicrous. Why are you storing an integer as a string?Quote:
Originally Posted by f.g
You can use it as-is. You just have to do it yourself manually. For example:You also have to think about what happens if the left most value is an F and you need to increment that. Do you grow your string longer, or do you treat it as overflow and apply some rule that you decide upon?Code:switch( ... )
{
case '0': ...
case '1': ...
...
case 'F': ...
}
Quzah.
Text files. Why do people use them? Beats me, but they always show up here complaining about flat files being bad. :PQuote:
Originally Posted by tabstop
Quzah.
Quote:
Originally Posted by quzah
Whoops, you're right. I forgot that strtoi is the only one left out of that family of functions. (I saw it years ago somewhere, but it seems to have died).
And given that we're passing this integer around to various and sundry other functions with and without 0x, the answer is probably even worse: "we've always used a string".Quote:
Originally Posted by quzah
Why store something in one byte what you can store it in five!Quote:
Originally Posted by tabstop
Code:char *p = "0xFF";
unsigned char byte = 0xFF;
Quzah.
hey, the firmware function that this needs to be passed to it some one else's work and non-negotiable. i should perhaps also point out that this is for a atmega128 microcontroller, so that might have something to do with it (the number has to exceed the largest unsigned int that the chip can contain).
So you want a built in simple way to work with numbers too big to work with normally? That's pretty silly if you stop and actually think about what you are asking. You are going to need to make your own method of handling this. Like I said, you need to also decide what happens when you are trying to increment something bigger than what your string allows.Quote:
Originally Posted by f.g
Quzah.
Are you writing the firmware/on the chip?
If not, then the firmware/chip limitations are completely irrelevant to you (apart from I/O). If you have to send it as a string, then send it as a string, but at no other time should this limitation enter your mind.
Code:if string is all Fs
realloc one more slot
set the left most spot to '1' and the rest to '0'
else
walk from the right most back to the left most, incrementing until you don't need to carry a number
Quzah.
yeah, they are written to the eeprom on the chip along with the application, then operates independently once powered up.
so quzah, these numbers would not be too large to work with normally, just in this context, i've just not written in c for a while and thought that there might be a better way.
Generally it's easier to use "big numbers" in assembler than C, because you can directly detect integer overflow.
Right, by "bigger than what you can do normally" means "on this particular setup, it's bigger than what you can normally do". If the only thing your implementation of C had was char, then trying to manipulate a two-byte value wouldn't be something you can normally do. In your case, your have something with what, 16 bit ints? So trying to use a 32 bit value is bigger than what it can normally do. Thus, you need a string or an array of said type, or whatever you choose.Quote:
Originally Posted by f.g
Now, you've already said you have to use a string and you can't change that, so obviously:There isn't a better way, because you just said you had to use a string. What you could do is reverse the order that they are stored in the string, and don't bother storing 0x (or in your case x0 if it was reversed).Quote:
Originally Posted by f.g
"0123456789abcdef" -> "fedcba907654321"That looks about right.Code:for( p = string; *p; p++ )
{
switch( tolower( *p ) )
{
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case 'a':
case 'b':
case 'c':
case 'd':
case 'e': (*p)++; return;
case '9': *p = 'a'; return;
case 'f' : *p = '0'; /* now you are carrying, if you run out of string, you need to do something */
}
}
Quzah.
thanks eveyone, i'll try it with a swith statement tomorrow.