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const char
introduction
- Read the pointer declarations right-to-left.
- const 放在 type 前或後是相同的
const char * const * is the same as char const * const *: a (non-const) pointer to a const pointer to a const char.const char * is the same as char const *: a (non-const) pointer to a const char.const char * * is the same as char const * *: a (non-const) pointer to a (non-const) pointer to a const char.
brief
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const X* p means “p points to an X that is const“: the X object can’t be changed via p.
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X* const p means “p is a const pointer to an X that is non-const“: you can’t change the pointer p itself, but you can change the X object via p.
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const X* const p means “p is a const pointer to an X that is const“: you can’t change the pointer p itself, nor can you change the X object via p.
const char* ptr; char const * ptr;
- 定義一個指向字元常量的指標
- ptr是一個指向 char* 型別的常量，所以不能用ptr來修改所指向的內容，換句話說，*ptr的值為const，不能修改
- 但是ptr的宣告並不意味著它指向的值實際上就是一個常量，而只是意味著對ptr而言，這個值是常量
- 實驗如下：ptr指向str，而str不是const，可以直接通過str變數來修改str的值，但是確不能通過ptr指標來修改。
char* const ptr;
- 定義一個指向字元的指標常數，即const指標
- 實驗得知，不能修改ptr指標，但是可以修改該指標指向的內容。
reference