Example of undefined behavior

Attempting to modify a string literal

cppreference c++ string literal 和 cppreference c string literals中，都对此进行了说明，cppreference c string literals对此进行了解释：

String literals are not modifiable (and in fact may be placed in read-only memory such as .rodata).

.rodata中ro的含义是read only。

Overflow and underflow

Update one variable more than once "in a sequence point"

在https://stackoverflow.com/a/14041847中给出了例子：

#include <iostream>
#define SQUARE(x) ((x) * (x))

int main()
{
int x = 2;
int y = SQUARE(x++);
std::cout << x << '\n'
          << y << '\n';

}

It is undefined behaviour to update one variable more than once "in a sequence point". A sequence point is not exactly the same as a statement, but for most intents and purposes, that's what we should consider it as. So doing x++ * x++ will update x twice, which is undefined and will probably lead to different values on different systems, and different outcome value in x as well.