Moving Past Delimiters

When we use the std::string::find() function to locate a delimiter within a string, it returns the index (position) of the first character of the delimiter. However, we often want to continue processing the string after the delimiter. This is why we use Start = End + 1.

Understanding String Indices

Remember that in C++, string indices start at 0. So, the first character of a string is at index 0, the second is at index 1, and so on.

When find() locates a delimiter like \n (newline) or , (comma), the End variable will hold the index of that delimiter character. If we want to move to the next part of the string, we need to skip over the delimiter. Adding 1 to End effectively moves us to the very next character, right after the delimiter.

Example

Let's consider a simple example with a comma-separated string:

1#include <iostream>
2#include <string>
3
4int main() {
5  std::string Data{"apple,banana,orange"};
6  size_t Start{0};
7
8  // Find the first comma
9  size_t End{Data.find(',')};
10
11  std::cout << "First part: " 
12    << Data.substr(Start, End - Start) << "\n";
13
14  // Move past the comma
15  Start = End + 1;
16
17  // Find the next comma
18  End = Data.find(',', Start);
19
20  std::cout << "Second part: " 
21    << Data.substr(Start, End - Start);
22}

1First part: apple
2Second part: banana

In this example:

1. End is initially set to the index of the first comma.
2. Data.substr(Start, End - Start) extracts "apple"
3. Start = End + 1 moves Start to the position after the comma, which is the first character of "banana".

If we didn't add 1, Start would keep pointing to the comma, and we'd get stuck processing the same part of the string repeatedly.