FP invalidContainer with substr()

[chrchr]

From solvespace-3.1-rc1/src/util.cpp:

void f(std::string& s) {
	if (!s.empty()) {
		std::string::iterator it = s.begin();
		while (isspace(*it)) it++;
		s = s.substr(it - s.begin());
	}
}

test.cpp:5:22: error: Using iterator to local container 's' that may be invalid. [invalidContainer]
        s = s.substr(it - s.begin());
                     ^
test.cpp:1:22: note: Passed to reference.
void f(std::string& s) {
                     ^
test.cpp:3:43: note: Iterator to container is created here.
        std::string::iterator it = s.begin();
                                          ^
test.cpp:4:23: note: Assuming condition is false
        while (isspace(*it)) it++;
                      ^
test.cpp:5:11: note: After calling 's=s.substr(it-s.begin())', iterators or references to the container's data may be invalid .
        s = s.substr(it - s.begin());
          ^
test.cpp:1:21: note: Variable created here.
void f(std::string& s) {
                    ^
test.cpp:5:22: note: Using iterator to local container 's' that may be invalid.
        s = s.substr(it - s.begin());
                     ^

Tested with ​https://github.com/danmar/cppcheck/commit/60c1eef6592f7ed49ccc2412923cc7ea9f04c67d.

[chrchr]

This also shows the error:

void f(std::string& s) {
	if (!s.empty()) {
		std::string::iterator it = s.begin();
		s = s.substr(it - s.begin());
	}
}

This is clean:

void f(std::string& s) {
	if (!s.empty()) {
		std::string::iterator it = s.begin();
		auto t = s.substr(it - s.begin());
		s = t;
	}
}

[pfultz2]

Fixed by: ​https://github.com/danmar/cppcheck/pull/4333