c++ - 基本的 C 风格字符串内存分配

Question

我正在使用现有代码开发一个项目，该代码主要使用 C++，但使用 C 风格的字符串。采取以下措施:

#include <iostream>
int main(int argc, char *argv[])
{
    char* myString = "this is a test";
    myString = "this is a very very very very very very very very very very very long string";
    cout << myString << endl;
    return 0;
}

这编译并运行良好，输出是长字符串。

但是我不明白为什么它有效。我的理解是

char* myString 

是一个指针，指向一个足够大的内存区域来保存字符串文字“this is a test”。如果是这样，那么我如何才能在同一位置存储更长的字符串？由于试图将长字符串塞入为较短字符串预留的空间，我预计它会在执行此操作时崩溃。

显然，对这里发生的事情存在基本的误解，所以我感谢任何帮助理解这一点。

Answer 1

你不是在改变内存的内容，你是在改变指针的值以指向一个不同的内存区域，它包含“这是一个非常非常非常非常非常非常非常非常非常非常长的字符串”。

请注意，char* myString 仅为指针分配足够的字节(通常为 4 或 8 个字节)。当您执行 char* myString = "this is a test"; 时，实际发生的是 甚至在您的程序开始之前，编译器在可执行文件中分配空间 image 并将 "this is a test" 放入内存中。然后当你做 char* myString = "this is a test"; 它实际上做的只是为指针分配足够的字节，并使指针指向它在编译时已经分配的内存, 在可执行文件中。

所以如果你喜欢图表:

char* myString = "this is a test";

(allocate memory for myString)

              ---> "this is a test"
            / 
myString---

                   "this is a very very very very very very very very very very very long string"

然后

myString = "this is a very very very very very very very very very very very long string";

                   "this is a test"

myString---
            \
              ---> "this is a very very very very very very very very very very very long string"