Proper way to create unique_ptr that holds an allocated array
c++, c++11, gcc, linux, unique-ptr
Solution
Using the `T[]` specialisation:
std::unique_ptr<unsigned char[]> testData(new unsigned char[16000]());
Note that, in an ideal world, you would not have to explicitly use `new` to instantiate a `unique_ptr`, avoiding a potential exception safety pitfall. To this end, C++14 provides you with the `std::make_unique` function template. See this excellent GOTW for more details. The syntax is:
auto testData = std::make_unique<unsigned char[]>(16000);
Problem
What is the proper way to create an unique_ptr that holds an array that is allocated on the free store? Visual studio 2013 supports this by default, but when I use gcc version 4.8.1 on Ubuntu I get memory leaks and undefined behaviour. The problem can be reproduced with this code: ``` #include <memory> #include <string.h> using namespace std; int main() { unique_ptr<unsigned char> testData(new unsigned char[16000]()); memset(testData.get(),0x12,0); return 0; } ``` Valgrind will give this output: ``` ==3894== 1 errors in context 1 of 1: ==3894== Mismatched free() / delete / delete [] ==3894== at 0x4C2BADC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==3894== by 0x400AEF: std::default_delete<unsigned char>::operator()(unsigned char*) const (unique_ptr.h:67) ==3894== by 0x4009D0: std::unique_ptr<unsigned char, std::default_delete<unsigned char> >::~unique_ptr() (unique_ptr.h:184) ==3894== by 0x4007A9: main (test.cpp:19) ==3894== Address 0x5a1a040 is 0 bytes inside a block of size 16,000 alloc'd ==3894== at 0x4C2AFE7: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==3894== by 0x40075F: main (test.cpp:15) ```