Why can't my str string be identified in sub scope?

Question

First to all, I found this source to get path of all files(Unicode) and it doesn't belong to me, I defined a string ( string str = "test"; ) and it's not detectable(cout << str;) in the function why is that happening?

#include <atlstr.h>
#include <iostream>
#include <string>
#include <functional>
#include <io.h>

using namespace std;

enum enumflags {
    ENUM_FILE = 1,
    ENUM_DIR,
    ENUM_BOTH
};

bool enumsubfiles(

    const std::wstring& dir_with_back_slant, //for example: L"C:\\", L"E:\\test\\"
    const std::wstring& filename, //for example: L"123.txt", L"*.exe", L"123.???"
    unsigned int maxdepth, //0 means not searching subdirectories, 1 means maximum depth of subdirectories is 1,
    //    pass -1 to search all the subdirectories.
    enumflags flags, //search files, directories, or both.
    std::function<bool(const std::wstring& dir_with_back_slant, _wfinddata_t& attrib)> callback)
    {
    _wfinddata_t dat;
    size_t hfile;
    std::wstring fullname = dir_with_back_slant + filename;
    std::wstring tmp;
    bool ret = true;

    hfile = _wfindfirst(fullname.c_str(), &dat);
    if (hfile == -1)
        goto a;
    do {
        if (!(wcscmp(L".", dat.name) && wcscmp(L"..", dat.name)))
            continue;
        if (((dat.attrib & _A_SUBDIR) && (!(flags & ENUM_DIR))) || ((!(dat.attrib & _A_SUBDIR)) && (!(flags & ENUM_FILE))))
            continue;
        ret = callback(dir_with_back_slant, dat);
        if (!ret) {
            _findclose(hfile);
            return ret;
        }
    } while (_wfindnext(hfile, &dat) == 0);
    _findclose(hfile);

a:

    if (!maxdepth)
        return ret;

    tmp = dir_with_back_slant + L"*";
    hfile = _wfindfirst(tmp.c_str(), &dat);
    if (hfile == -1)
        return ret;
    do {
        if (!(wcscmp(L".", dat.name) && wcscmp(L"..", dat.name)))
            continue;
        if (!(dat.attrib & _A_SUBDIR))
            continue;
        tmp = dir_with_back_slant + dat.name + L"\\";
        ret = enumsubfiles(tmp, filename, maxdepth - 1, flags, callback);
        if (!ret) {
            _findclose(hfile);
            return ret;
        }

    } while (_wfindnext(hfile, &dat) == 0);
    _findclose(hfile);

    return ret;
}
int _tmain(int argc, _TCHAR* argv[])
{
    string str = "test";

    enumsubfiles(L"B:\\", L"*.txt", -1, ENUM_FILE, [](const std::wstring& dir_with_back_slant, _wfinddata_t& attrib) -> bool {
        wcout << dir_with_back_slant << attrib.name << '\n';
        cout << str;
        return true; //return true to continue, return false to abort searching.
    });

    return 0;
}

Honestly, I do not understand anything from this source, I want to define a variable at the beginning of the int t_main() and call it inside the function and I don't want to define it in the function

Why would it be visible? It's in an unrelated scope. Did you mean to use a _lambda capture_? You should narrow your problem down to something small. — Asteroids With Wings, Oct 22 '20 at 15:48
If you want to acces `str` in the lambda you either need to capture it or pass it as parameter. — 463035818_is_not_an_ai, Oct 22 '20 at 15:49
Does this answer your question? [How can I access local variables from inside a C++11 anonymous function?](https://stackoverflow.com/questions/7100889/how-can-i-access-local-variables-from-inside-a-c11-anonymous-function) — Yksisarvinen, Oct 22 '20 at 15:50
how to capture or path it ? I tried to path it but I couldn't — Malek, Oct 22 '20 at 15:54
I have no idea what do you mean by "path it", but the capture is simply `[str](...){...}` — Yksisarvinen, Oct 22 '20 at 16:05

score 3 · Accepted Answer · answered Oct 22 '20 at 16:24

Because str is not known in the scope where it is used.

string str = "test";

Unknown:

enumsubfiles(L"B:\\", L"*.txt", -1, ENUM_FILE, [](const std::wstring& dir_with_back_slant, _wfinddata_t& attrib) -> bool 
{ // str is unknown in this scope
    wcout << dir_with_back_slant << attrib.name << '\n';
    cout << str;
    return true; //return true to continue, return false to abort searching.
});

To make it known you can capture it (in the lambda expression capture list, [...]):

enumsubfiles(L"B:\\", L"*.txt", -1, ENUM_FILE, [str](const std::wstring& dir_with_back_slant, _wfinddata_t& attrib) -> bool 
{ // str is known in this scope
    wcout << dir_with_back_slant << attrib.name << '\n';
    cout << str;
    return true; //return true to continue, return false to abort searching.
});

Why can't my str string be identified in sub scope?

1 Answers1