具有字符串成员的结构的动态数组

Question

I've created in my program a dynamic array of struct which members are also strings. I've some doubts about safe behaviour in manipulating strings inside the dynamically allocated struct. Am I allowed to update or concatenate strings as I do with normal string variables? Do I have to concern about the boundaries of the allocated memory of the struct?

To make it a bit clear, I've something like the following pseudocode :

First I've the struct declaration

struct myStruct
{
    ...
    int data1;
    int data2;
    std::string myString1;
    std::string myString2;
    ...
}

Then the struct is allocated

mystruct testStruct*;
testStruct = new mystruct [MAX_DEPTH];

The strings are initialized

for(int i=0; i<MAX_DEPTH; i++)
{
    ...
    testStruct[i].myString1 = "";
    testStruct[i].myString2 = "";
    ...
}

During the program cycles, the strings values are assigned and updated

...
testStruct[N].myString1 = "Some text";
...
testStruct[N].myString1 += "Some other text";
...

Here I'm not sure to deal correctly with the allocated memory.

Are these assignments correct, and safe, even inside a dynamically allocated array of struct? I'm risking to break the boundary of dynamic allocated memory for myStruct variable?

Thanks

EDIT: I've corrected the [i] wrongly placed in the psuedocode.

Answer 1

For starters the expressions within the loop are incorrect

for(int i=0; i<MAX_DEPTH; i++)
{
    ...
    testStruct.myString1[i] = "";
    testStruct.myString2[i] = "";
    ...
}

You mean

for(int i=0; i<MAX_DEPTH; i++)
{
    ...
    testStruct[i].myString1 = "";
    testStruct[i].myString2 = "";
    ...
}

But in any case the loop is redundant because the objects of the type std::string were already default initialized when the memory for the array of structures were allocated.

As for these statements

testStruct.myString1[N] = "Some text";
...
testStruct.myString1[N] += "Some other text";

then again you need to apply the subscript operator to the pointer testStruct . For example

testStruct[N].myString1 = "Some text";
...
testStruct[N].myString1 += "Some other text";

I'm risking to break the boundary of dynamic allocated memory for myStruct variable?

If you will use an index that is greater than or equal to MAX_DEPTH with the pointer testStruct then it is evident that there will be undefined behavior,

Answer 2

class string is implemented in the following manner:

namespace std {
    template <typename charT,
              typename traits = char_traits<charT>,
              typename Allocator = allocator<charT>>
            class basic_string;

    typedef basic_string<char> string;
}

The third argument is the memory model used by the string class which handles the allocation and deallocation of memory.