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In a little while
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 Posted: Sun Nov 19, 2006 10:11 am Post subject: how to calculate the difference between 2 addresses ? |
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thanks |
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Salt_Peter
Guest
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| Posted: Sun Nov 19, 2006 10:11 am Post subject: Re: how to calculate the difference between 2 addresses ? |
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In a little while wrote:
That depends of the types at the addresses involved. If you attempt to
calculate the offset of 2 integers, for example, you need to substract
their corresponding address and then mutiply by sizeof(int) in order to
obtain a byte-size quantitative value (if thats what you are getting
at).
An object's pointer is bound to its type. Thats how a pointer does
++ptr to find the next element.
So you need to explain what you mean by difference between 2 addresses,
because in C++ speak, that means "in terms of the objects involved".
And you can forget using void* for that too.
#include <iostream>
template< typename T >
size_t difference(const T& r_lhs, const T& r_rhs)
{
return (&r_lhs - &r_rhs) * sizeof(T);
}
int main()
{
int m(0);
int* p_m = &m;
std::cout << "p_m = " << p_m << std::endl;
int o(0);
int* p_o = &o;
std::cout << "p_o = " << p_o << std::endl;
std::cout << "difference(p_m, p_o) in bytes: ";
std::cout << difference(p_m, p_o) << std::endl;
return 0;
}
/*
p_m = 0x7fff628c8c54
p_o = 0x7fff628c8c44
difference(p_m, p_o) in bytes: 16
*/
Please don't be confused by the above program. This is not something a
C++ programmer needs to do in typical C++ code. Also, a programmer
never relies on a primitive to have some given size. |
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rTrenado
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| Posted: Sun Nov 19, 2006 10:12 am Post subject: Re: how to calculate the difference between 2 addresses ? |
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Address1 - Address2?
In a little while wrote:
> thanks |
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John Carson
Guest
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| Posted: Sun Nov 19, 2006 10:12 am Post subject: Re: how to calculate the difference between 2 addresses ? |
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"In a little while" <cppcoder1234567890 (AT) yahoo (DOT) com> wrote in message
news:1163917662.107646.326020 (AT) h48g2000cwc (DOT) googlegroups.com
Cast each of them to an integer type and perform the subtraction.
To cover ever possible address value, you will need a pointer-sized integer
type and it will need to be unsigned.
Since it is unsigned, you can only subtract the smaller from the larger, so
you will need to do an if() test to establish which is smaller before doing
the subtraction.
PS. It aids readability if you repeat your question in the body of your
post.
--
John Carson |
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