Vector's of unsigned char iterators not working - c++

Question

I wanna to cut CRLF at end of the vector, but my code is not working (at first loop of while - equal is calling and returns false). In debug mode "i" == 0 and have "ptr" value == "0x002e4cfe"
string testS = "\r\n\r\n\r\n<-3 CRLF Testing trim new lines 3 CRLF->\r\n\r\n\r\n";
vector<uint8> _data; _data.clear();
_data.insert(_data.end(), testS.begin(), testS.end());
vector<uint8>::iterator i = _data.end();
uint32 bytesToCut = 0;
while(i != _data.begin()) {
if(equal(i - 1, i, "\r\n")) {
bytesToCut += 2;
--i; if(i == _data.begin()) return; else --i;
} else {
if(bytesToCut) _data.erase(_data.end() - bytesToCut, _data.end());
return;
}
}
Thanks a lot for your answers. But i need version with iterators, because my code is used when i parsing chunked http transfering data, which is writed to vector and i need func, which would take a pointer to a vector and iterator defining the position to remove CRLF backwards. And all my problems, i think, apparently enclosed in iterators.

Answer 1

Your code is invalid at least due to setting incorrect range in algorithm std::equal
if(equal(i - 1, i, "\r\n")) {
In this expression you compare only one element of the vector pointed by iterator i - 1 with '\r'. You have to write something as
if(equal(i - 2, i, "\r\n")) {
If you need to remove pairs "\r\n" from the vector then I can suggest the following approach (I used my own variable names and included testing output):
std::string s = "\r\n\r\n\r\n<-3 CRLF Testing trim new lines 3 CRLF->\r\n\r\n\r\n";
std::vector<unsigned char> v( s.begin(), s.end() );
std::cout << v.size() << std::endl;
auto last = v.end();
auto prev = v.end();
while ( prev != v.begin() && *--prev == '\n' && prev != v.begin() && *--prev == '\r' )
{
last = prev;
}
v.erase( last, v.end() );
std::cout << v.size() << std::endl;

Answer 2

instead if re inventing th wheel you can the existing STL algo with something like:
std::string s;
s = s.substr(0, s.find_last_not_of(" \r\n"));

Answer 3

If you need to just trim '\r' & '\n' from the end then simple substr will do:
std::string str = "\r\n\r\n\r\nSome string\r\n\r\n\r\n";
size_t newLength = str.length();
while (str[newLength - 1] == '\r' || str[newLength - 1] == '\n') newLength--;
str = str.substr(0, newLength);
std::cout << str;
Don't sweat small stuff :)
Removing all '\r' and '\n' could be simple as (C++03):
#include <iostream>
#include <string>
#include <algorithm>
int main() {
std::string str = "\r\n\r\n\r\nSome string\r\n\r\n\r\n";
str.erase(std::remove(str.begin(), str.end(), '\r'), str.end());
str.erase(std::remove(str.begin(), str.end(), '\n'), str.end());
std::cout << str;
}
or:
bool isUnwantedChar(char c) {
return (c == '\r' || c == '\n');
}
int main() {
std::string str = "\r\n\r\n\r\nSome string\r\n\r\n\r\n";
str.erase(std::remove_if(str.begin(), str.end(), isUnwantedChar), str.end());
std::cout << str;
}

Answer 4

First of all, your vector initialization is ... non-optimal. All you needed to do is:
string testS = "\r\n\r\n\r\n<-3 CRLF Testing trim new lines 3 CRLF->\r\n\r\n\r\n";
vector<uint8> _data(testS.begin(), testS.end());
Second, if you wanted to remove the \r and \n characters, you could have done it in the string:
testS.erase(std::remove_if(testS.begin(), testS.end(), [](char c)
{
return c == '\r' || c == '\n';
}), testS.end());
If you wanted to do it in the vector, it is the same basic process:
_data.erase(std::remove_if(_data.begin(), _data.end(), [](uint8 ui)
{
return ui == static_cast<uint8>('\r') || ui == static_cast<uint8>('\n');
}), _data.end());
Your problem is likely due to the usage of invalidated iterators in your loop (that has several other logical issues, but since it shouldn't exist anyway, I won't touch on) that removes elements 1-by-1.
If you wanted to remove the items just from the end of the string/vector, it would be slightly different, but still the same basic pattern:
int start = testS.find_first_not_of("\r\n", 0); // finds the first non-\r\n character in the string
int end = testS.find_first_of("\r\n", start); // find the first \r\n character after real characters
// assuming neither start nor end are equal to std::string::npos - this should be checked
testS.erase(testS.begin() + end, testS.end()); // erase the `\r\n`s at the end of the string.
or alternatively (if \r\n can be in the middle of the string as well):
std::string::reverse_iterator rit = std::find_if_not(testS.rbegin(), testS.rend(), [](char c)
{
return c == '\r' || c == '\n';
});
testS.erase(rit.base(), testS.end());