CODEWITHSUNDEEP
c++stringcomboboxstd
user565739
user565739

Reputation: 1332

compare typed string in a combobox with its items

Suppose I have 20 string of different length, each of them is supposed to obtained similar to the following:

TCHAR *itemText[...];
SendMessage(hwndCombobox, CB_GETLBTEXT, i, (LPARAM)itemText);

Since I have an index for the items, I would like to use the above code in a for loop. But because each item has different length, I can't use something like:

int itemLength = SendMessage(hwndCombobox, CB_GETLBTEXTLEN, i, 0);
TCHAR *itemText[itemLength];

Since using the message CB_GETLBTEXTLEN require the length at first, it is necessary to get the length. I know I can just use, for example, TCHAR *itemText[1024];, but I don't like this way personally.

I also tried to use new and delete, and other people suggest me to use vector along with std::string instead, as in this post delete pointers created by new in CallBack Function, but that leads to another problem in that the LPARAM parameter needed for CB_GETLBTEXT requires A pointer to the buffer that receives the string., so the following code doesn't work, since the last parameter is std::string, rather than a pointer which receives strings:

int i;
Vec<std::string> itemText;
for (i = 0; i < itemCount; i++) {
    ......... // Don't know how to initialize a string with a specified length.
    SendMessage(win->hwndFindBox, CB_GETLBTEXT, i, (LPARAM)itemText.At(i));
}

I don't neither know how to initialize a std::string str with a specified length.

In fact, I would like to compare the typed string in the edit control of a combobox control with the items on this combobox. Do you have any suggestion to solve this problem or to do what I want to do?

Upvotes: 0

Views: 555

Answers (1)

jamesdlin
jamesdlin

Reputation: 90175

You might have misunderstood suggestions to use std::vector with std::string. You should use std::vector<TCHAR> as a temporary buffer when reading the ComboBox item text (because you cannot write directly to the internal buffer used by std::basic_string), and then you can copy that into a std::basic_string<TCHAR> afterward if desired:

std::basic_string<TCHAR> s;
int itemLength = SendMessage(hwndCombobox, CB_GETLBTEXTLEN, i, 0);
if (itemLength != CB_ERR)
{
    std::vector<TCHAR> buf(itemLength + 1 /* for NUL */);
    SendMessage(hwndCombobox, CB_GETLBTEXT, i, reinterpret_cast<LPARAM>(&buf[0]));

    s = &buf[0];
}

This works because std::vector is guaranteed to use contiguous memory, so &buf[0] should be equivalent to an array (assuming that buf is not empty, but in this case, we guarantee that it has at least 1 element).

Upvotes: 1

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