C++ arrays [from:to] - c++

Question

How can i do that in C++?
in python is
example = [u'one', u'two', u'three', u'four']
print example[1:3]
How can i do that in C++ (i missing this function)
I need rewrite this to C++
while i<len(a)-1:
if (a[i]=='\x00' or a[i]=='\x04') and (eval("0x"+(a[i-1].encode("hex"))) in range(32-(4*eval((a[i].encode("hex")))),128-(12*eval((a[i].encode("hex")))))):
st+=a[i-1:i+1]
i+=2;continue
elif st=='':
i+=1;continue
elif len(st)>=4 and (a[i-1:i+1]=='\x00\x00' or a[i-1:i+1]=='\x0a\x00' or a[i-1:i+1]=='\x09\x00' or a[i-1:i+1]=='\x0d\x00'):
s.STRINGS.append([st.decode("utf-16le"),0xffffff])
s.INDEX.append(iCodeOffset+i-1-len(st))
st=''
i=i-1;continue
else:
st=''
i=i-1;continue
I need list of strings from binary files without using string.exe
THX for advance
Benecore

Answer 1

Here is a function that returns a new spliced vector given then old one. It does only the most basic splicing (from:to), and only in one direction (not sure if from is greater than to but I believe python reverses the output).
template<typename T>
std::vector<T> splice(const std::vector<T> in, int from, int to)
{
if (to < from) std::swap(to, from);
std::vector<T> ret(to - from + 1);
for (to -= from; to + 1; to--)
{
ret[to] = in[from + to];
}
return ret;
}

Answer 2

First of all, there is no immediate replacement for this in C++, as C++ is not python and has its own idioms that work differently.
To begin with, for strings you can use the specific std::string::substr.
For more generic containers you should know C++ usually works iterator based when operating on elements of said container. For example suppose you want to compare elements in a vector, you'd do something like the following:
#include <iostream>
#include <algorithm>
#include <vector>
int main()
{
std::vector<int> a = {1,2,3,4};
std::vector<int> b = {1,2,10,4};
std::cout << "Whole vectors equal? " << (std::equal(a.begin(), a.end(), b.begin())?"yes":"no") << std::endl;
}
Now, suppose we only want to compare the first two values (like [:2]), Then we would rewrite the last statement to something like this:
std::cout << "First 2 values equal? " << (std::equal(a.begin(), a.begin()+2, b.begin())?"yes":"no") << std::endl;
Suppose we want to compare the last two values we would do this:
std::cout << "Last 2 values equal? " << (std::equal(a.end()-2, a.end(), b.begin())?"yes":"no") << std::endl;
See the pattern emerging? x.begin()+i,x.begin()+j is roughly equal to [i:j], and x.end()-i,x.end()-j) is roughly equal to [-i,-j]. Note that you can mix these of course.
So in general when working on containers you will work on a range of iterators and this iterator range can be specified very much alike to python's list splicing. It is more verbose and it is another idiom (spliced lists are lists again but iterators are no containers), but you get the same result.
Some final notes:
I wrote x.begin() to make the code a bit clearer, you can also write std::begin(x), which is more generic and also works on arrays. The same goes for std::end
Take a look to the algorithms library before writing your own for loops over iterators.
Yes you can write your own for loops (something like for(auto it = a.begin(); it != a.end(); it++), but often it's easier and more consistent to pass a function or lambda to std::foreach
Really remember C++ is not python or vice versa.