C ++字符串std :: out_of_range：basic_string :: substr

Question

I am making a program with a function that checks for the adjacent characters of a string in an array. I do this with the substring function (among other things), but I need a way to use an if statement to avoid empty strings, like finding the trailing character of the first character in a string. I am new to using strings instead of char[] . I want some that essentially does this:

if (!Empty ( strings[1].substr(0-1,0) )) {
     std::cout<<"char to left of substr(0)="<<strings[1].substr(0-1,0);
}

When I try to reference a non existent char, I get the runtime error:

libc++abi.dylib: terminating with uncaught exception of type std::out_of_range:
basic_string::substr
Abort trap: 6

Answer 1

Oh, a substring starting at index -1, of length 0.

Or, since the first argument is unsigned, it starts at std::numeric_limits<size_t>::max() .

Anyway.