c++ - 指针可以用于访问内存中的任意区域吗？

Question

我对 C++ 和指针非常陌生。

#include <iostream>

using namespace std;

int main() {
    char* c = "my name jeff";
    int i = 0;
    while (true) {
        cout << *(c + i++);
    }
    return 0;
}

输出是“my name jeff”，后跟许多随机字符，偶尔有意义。我实际上是在访问计算机中的内存吗？为什么可以从字符串初始化指针？

Answer 1

来自 https://eel.is/c++draft/expr#add-4

When an expression J that has integral type is added to or subtracted from an expression P of pointer type, the result has the type of P.

(4.1) If P evaluates to a null pointer value and J evaluates to 0, the result is a null pointer value.

(4.2) Otherwise, if P points to an array element i of an array object x with n elements ([dcl.array]),77 the expressions P + J and J + P (where J has the value j) point to the (possibly-hypothetical) array element i + j of x if 0 ≤ i + j ≤ n and the expression P - J points to the (possibly-hypothetical) array element i − j of x if 0 ≤ i − j ≤ n .

(4.3) Otherwise, the behavior is undefined.

因此，使用 "my name jeff"(属于 const char[13] 类型(带有额外的 '\0' ))，一旦你执行了 c[14]，你就有了 UB。