Get string content from string pointer C++ - c++

Question

so I'm working on a project that I have to read contents from a file and then analyze them. But I'm having a problem with getting the string out of a pointer that contains the address to what I need.
string lePapel(vector<char> vec){
string *str, s;
int i, j = 0;
vector<char> aux;
aux.resize(6);
for (i = 57; i <= 62; i++){
aux[j] = vec[i];
j++;
}
str = new string[aux.size()];
for (i = 0; i < 6; i++){ str[i] = aux[i]; }
return s;
}
So, the file contains in the array positions from 57 to 62 the word: ABCB4, but when returning the string s my output is A only as expected because of the pointer.
The thing is that I have been trying to find a solution and storing the whole content from vec[57] to vec[64] into the string s and returning it, and the closest that I got to returning anything plausible was using a pointer.
So, now to my question, how can I iterate the *str pointer and copy the whole content to s and return it?
Thanks in advance

Answer 1

I'd suggest you to not use pointers on string in your case. The following code is probably what you want :
#include <iostream>
#include <string>
#include <vector>
using namespace std;
string lePapel(vector<char> vec){
int j = 0;
vector<char> aux;
aux.resize(6);
for (int i = 57; i <= 62; i++){
aux[j] = vec[j];
j++;
}
string str;
str.reserve(6);
for (int i = 0; i < 6; i++){ str.push_back(aux[i]); }
return str;
}
int main() {
char x[5] = {'A', 'B', 'C', 'B', '4'};
vector<char> vec(x, x + 5);
string s = lePapel(vec);
cout << s;
return 0;
}
Tested here : Tested code
About reserving space to your vector : c++ vector::reserve
Same for strings : reserve for strings

Answer 2

The dynamic array of string objects and the whole aux vector seem completely needless here (unless there's some other purpose for them in your code). Additionally, str is currently causing a memory leak because you never delete it when you're finished.
A much simpler approach is just to append the characters one-at-a-time to the s string object (assuming it's a std::string):
string lePapel(vector<char> vec) {
string s;
for (int i = 57; i <= 62; i++) {
s += vec[i];
}
return s;
}
There are various ways to make the code even shorter (and more efficient) than that though, if you really want to.
EDIT: If you still need/want to iterate your dynamic array and concatenate the contents into s, here's how you could do it:
for (i = 0; i < 6; i++) s += str[i];
delete [] str; //<-- very important!

Answer 3

Short answer, you don't want a string * you want a char *. What you created is a string array. String objects contain a pointer to the char * data you are trying to capture. Also, the sizeof(std::string) (8 bytes in size) is a lot bigger than sizeof(char) (1 byte in size) the second character you store is 8 bytes away from the first character instead of being adjacent.
There are a lot of other C++ style and safety concerns, but I'll stick with the question. ;)