c++ - Stringstream to Vector<char> throws std::bad_alloc

Question

I was tinkering with Boost Property Tree a bit, and I came across this example. I needed to convert the final result to vector, so I just added one more line after

write_json(ss, root);

like this:

std::vector<char> testVec(std::begin(ss.str()), std::end(ss.str()));

I have also tried this instead:

std::string someString = ss.str()
char* someArray = (char*)someString.c_str();
std::vector<char> someVec(someArray, someArray+sizeof(someArray));

In both the cases, I am getting this error:

terminate called after throwing an instance of 'std::bad_alloc'
what():  std::bad_alloc

Any hints what I am doing wrong? It is not a problem of property tree, I gather. It is a problem of string to vector conversion. I guess this makes sense, because vectors are only supposed to be one dimensional, but I have no clue how to convert that string to vector and get it back again.

Answer 1

This fails:

std::vector<char> testVec(std::begin(ss.str()), std::end(ss.str())); 

because the std::begin() and std::end() are not associated with same std::string instance. The ss.str() returns a new std::string instance each time, it does not return a std::string& to some internal member.

This is incorrect:

std::vector<char> someVec(someArray, someArray+sizeof(someArray)); 

because sizeof(someArray) is sizeof(char*). If there is less than sizeof(char*) elements in someArray an attempt will be made to read memory that should not.

A possible solution:

std::string someString = ss.str();
std::vector<char> someVec(someString.begin(), someString.end());