output char* to std::string C++

Question

So given:

struct MemoryStruct {
    char *memory;
    size_t size;
};

char* memory holds a curl return, XML doc.

I am doing:

if(chunk.memory) {
    std::cout << "char size is " << sizeof(chunk.memory) << std::endl;
    std::string s = "";
    for (int c = 0; c<sizeof(chunk.memory); c++) {
        s.push_back(chunk.memory[c]);
    }
    std::cout << "s: " << s.c_str() << std::endl;
}

I am only getting back <?xm

So sizeof() I think is return the total bytes in the char*

How do I get what the actual value is a char* . So basically the whole curl return. Which is 5 lines of XML?

Answer 1

sizeof(chunk.memory) will give always you size of a pointer which in your case seems to be 4. That's why you see only 4 characters in your std::string.

If your curl return or whatever else is terminated by \\0 , then you can directly do the following

std::string s(chunk.memory);

If your char * is not terminated by \\0 , then you need to know the length of the string - you cannot use sizeof(chunk.memory) for this. If your chunk.size contains the correct size, then you can use

std::string s(chunk.memory, chunk.size);

Answer 2

std::string constructor can accept char* and data length ( see the docs ); Example:

  std::string s(chunk.memory, chunk.size);

So container will pre-allocate need space for your string and initialize with it.

Answer 3

In MemoryStruct memory is the pointer to the first returned character and size is the number of characters returned. You want to initialize a string with this data so you will need to do:

s.assign(chunk.memory, chunk.size);