爲什麼包含字符串常量的初始化程序有效初始化一個char數組？

Question

事實證明char c[] = {"a"};在C++03和C++11中都是完全有效的。

我不希望它是，因爲它是char而不是char const*的數組，我期望一個括號初始化程序要求它的每個「項目」都有一個兼容的類型。它有一個項目，這是一個char const*而不是一個char。

那麼是什麼讓這個初始化有效？是否有這樣的理由？

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^{同樣，char c[] = {"aa"};編譯，並打印c結果在輸出 「aa」。}

^{我會期望char c[]{"a"}是在C++ 11，當然有效，但它是不一樣的！同樣，char c[] = {'a'}在兩者中都是顯而易見的，因爲是char c[] = "a"。}

Answer 1

標量類型也可以使用花括號進行初始化（就像結構和數組一樣）。

struct S { int x, char c }; 
S s = {5, 'a'}; 

int arr[] = {5, 6, 7}; 

/* (my guess) out of consistency */ 
int z = { 4 }; 

而且因爲字符串文字可以被分配到字符數組的指針和

char arr[] = "literal"; 
char* ptr = "another"; 

似乎擬合允許char arr[] = { "literal" };了。

Answer 2

雖然它可能不一定是直觀的，但它只是是允許的;兩種標準都有明確的規定：

[2003: 8.5.2/1]:A char array (whether plain char , signed char , or unsigned char) can be initialized by a string-literal (optionally enclosed in braces); a wchar_t array can be initialized by a wide string-literal (optionally enclosed in braces); successive characters of the string-literal initialize the members of the array. [..]

[n3290: 8.5.2/1]:A char array (whether plain char , signed char , or unsigned char), char16_t array, char32_t array, or wchar_t array can be initialized by a narrow character literal, char16_t string literal, char32_t string literal, or wide string literal, respectively, or by an appropriately-typed string literal enclosed in braces. Successive characters of the value of the string literal initialize the elements of the array.

雖然我不能解釋爲什麼委員會這樣做。

Answer 3

我想這是C兼容性？實際上，T x = { value of T };也適用於其他類型的T。在C99標準中，

6.7.8/11: The initializer for a scalar shall be a single expression, optionally enclosed in braces.

6.7.8/14: An array of character type may be initialized by a character string literal, optionally enclosed in braces.

6.7.8/15: An array with element type compatible with wchar_t may be initialized by a wide string literal, optionally enclosed in braces.

我不知道爲什麼C有這個雖然。