Task: Text between
C++: #include <iostream>

std::ostream& operator<<(std::ostream& out, const std::string& str) {
    return out << str.c_str();
}

std::string textBetween(const std::string& source, const std::string& beg, const std::string& end) {
    size_t startIndex;
    if (beg == "start") {
        startIndex = 0;
    } else {
        startIndex = source.find(beg);
        if (startIndex == std::string::npos) {
            return "";
        }
        startIndex += beg.length();
    }

    size_t endIndex = source.find(end, startIndex);
    if (endIndex == std::string::npos || end == "end") {
        return source.substr(startIndex);
    }

    return source.substr(startIndex, endIndex - startIndex);
}

void print(const std::string& source, const std::string& beg, const std::string& end) {
    using namespace std;
    cout << "text: '" << source << "'\n";
    cout << "start: '" << beg << "'\n";
    cout << "end: '" << end << "'\n";
    cout << "result: '" << textBetween(source, beg, end) << "'\n";
    cout << '\n';
}

int main() {
    print("Hello Rosetta Code world", "Hello ", " world");
    print("Hello Rosetta Code world", "start", " world");
    print("Hello Rosetta Code world", "Hello ", "end");
    print("<text>Hello <span>Rosetta Code</span> world</text><table style=\"myTable\">", "<text>", "<table>");
    print("<table style=\"myTable\"><tr><td>hello world</td></tr></table>", "<table>", "</table>");
    print("The quick brown fox jumps over the lazy other fox", "quick ", " fox");
    print("One fish two fish red fish blue fish", "fish ", " red");
    print("FooBarBazFooBuxQuux", "Foo", "Foo");

    return 0;
}

VB: Option Explicit

Private Const STRING_START As String = "Start"
Private Const STRING_END As String = "End"

Sub Main()
Dim Text As String, First As String, Last As String, Output As String

    Text = "Hello Rosetta Code world"
        First = "Hello "
            Last = " world"
    Output = "1- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "Hello Rosetta Code world"
        First = "Start"
            Last = " world"
    Output = Output & "2- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "Hello Rosetta Code world"
        First = "Hello "
            Last = "End"
    Output = Output & "3- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "</div><div style=\""chinese\"">你好嗎</div>..."
        First = "<div style=\""chinese\"">"
            Last = "</div>"
    Output = Output & "4- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "<text>Hello <span>Rosetta Code</span> world</text><table style=\""myTable\"">"
        First = "<text>"
            Last = "<table>"
    Output = Output & "5- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "<table style=\""myTable\""><tr><td>hello world</td></tr></table>"
        First = "<table>"
            Last = "</table>"
    Output = Output & "6- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "The quick brown fox jumps over the lazy other fox"
        First = "quick "
            Last = " fox"
    Output = Output & "7- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "One fish two fish red fish blue fish"
        First = "fish "
            Last = " red"
    Output = Output & "8- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "FooBarBazFooBuxQuux"
        First = "Foo"
            Last = "Foo"
    Output = Output & "9- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "</div><div style=\""chinese\"">你好嗎..."
        First = "<div style=\""chinese\"">"
            Last = "</div>"
    Output = Output & "10- " & Text_Between(Text, First, Last) & vbCrLf

    Text = ""
        First = "Start"
            Last = "End"
    Output = Output & "11- " & Text_Between(Text, First, Last) & vbCrLf

    Text = "Hello Rosetta Code world"
        First = "Start"
            Last = "End"
    Output = Output & "12- " & Text_Between(Text, First, Last)

    Debug.Print Output
End Sub

Private Function Text_Between(T$, F$, L$) As String
Dim i As Long
    i = InStr(T, L) + 1
    Select Case True
        Case T = "", F = "", InStr(T, F) = 0 And F <> STRING_START
            Text_Between = ""
        Case F = STRING_START And L = STRING_END
            Text_Between = T
        Case F = STRING_START
            Text_Between = Mid(T, 1, InStr(T, L) - 1)
        Case L = STRING_END, InStr(T, L) = 0, InStr(T, L) < InStr(T, F) And InStr(i, T, L) = 0
            Text_Between = Mid(T, Len(F) + InStr(T, F))
        Case F = L
            Text_Between = Mid(T, Len(F) + InStr(T, F), InStr(i, T, F) - Len(F) - 1)
        Case Else
            Text_Between = Mid(T, Len(F) + InStr(T, F), InStr(InStr(T, F), T, L) - (Len(F) + InStr(T, F)))
    End Select
End Function