C++ “a”和“a”有什么区别？
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What is the difference between 'a' and "a"?
提问by james
I am learning C++ and have got a question that I cannot find the answer to.
我正在学习 C++ 并且遇到了一个我找不到答案的问题。
What is the difference between a charconstant (using single quotes) and a string constant (with double quotes)?
char常量（使用单引号）和字符串常量（使用双引号）有什么区别？
All my search results related to char arrays vs std::string. I am after the difference between 'a'and "a".
我所有的搜索结果都与 char 数组 vs std::string. 我之间的差额后'a'和"a"。
Would there be a difference in doing the following:
执行以下操作是否有区别：
cout << "a";
cout << 'a';
回答by Keith Thompson
'a'is a character literal. It's of type char, with the value 97 on most systems (the ASCII/Latin-1/Unicode encoding for the letter a).
'a'是字符文字。它的类型为char，在大多数系统上值为 97（字母的 ASCII/Latin-1/Unicode 编码a）。
"a"is a string literal. It's of type const char[2], and refers to an array of 2 chars with values 'a'and '\0'. In most, but not all, contexts, a reference to "a"will be implicitly converted to a pointer to the first character of the string.
"a"是字符串文字。它的类型为const char[2]，并且指的是一个由 2 组成char的数组，其值为'a'和'\0'。在大多数（但不是全部）上下文中，对的引用"a"将隐式转换为指向字符串第一个字符的指针。
Both
两个都
cout << 'a';
and
和
cout << "a";
happen to produce the same output, but for different reasons. The first prints a single character value. The second successively prints all the characters of the string (except for the terminating '\0') -- which happens to be the single character 'a'.
碰巧产生相同的输出，但出于不同的原因。第一个打印单个字符值。第二个连续打印字符串的所有字符（终止符除外'\0'）——恰好是单个字符'a'。
String literals can be arbitrarily long, such as "abcdefg". Character literals almost always contain just a single character. (You can have multicharacter literals, such as 'ab', but their values are implementation-defined and they're very rarely useful.)
字符串文字可以是任意长的，例如"abcdefg". 字符文字几乎总是只包含一个字符。（您可以使用多字符文字，例如'ab'，但它们的值是实现定义的，并且很少有用。）
(In C, which you didn't ask about, 'a'is of type int, and "a"is of type char[2](no const)).
（在 C 中，你没有问过，'a'是 type int，并且"a"是char[2](no const)类型）。
回答by Ry-
"a"is an array of characters that just happens to only contain one character, or two if you count the \0at the end. 'a'is one character. They're not the same thing. For example:
"a"是一个字符数组，恰好只包含一个字符，或者如果你\0在最后算上两个字符。'a'是一个字符。他们不是一回事。例如：
#include <stdio.h>
void test(char c) {
printf("Got character %c\n", c);
}
void test(const char* c) {
printf("Got string %s\n", c);
}
int main() {
test('c');
test("c");
}
This will use two different overloads; see http://codepad.org/okl0UcCNfor a demo.
这将使用两种不同的重载；有关演示，请参阅http://codepad.org/okl0UcCN。
回答by Hot Licks
Single quotes are used to surround character literals. Double quotes are used to surround string (character array) literals.
单引号用于包围字符文字。双引号用于包围字符串（字符数组）文字。
Many interfaces, such as cout <<, accept either.
许多接口，例如cout <<，都接受。
回答by ThomasMcLeod
A single quoted 'a'is a literal of type char. A double quoted "a"is a null-terminated string literal of chars.
单引号'a'是类型的文字char。双引号"a"是chars 的以空字符结尾的字符串文字。
回答by user3425449
- "a" -> it denotes it is a string. in c++ string is a collection of characters array.
- so string is terminated by delimiter '\0'it indicates the end of string.
- so its size would be 2 because 1-byte for "a" and 1-byte for '\0'
- "a" -> 它表示它是一个字符串。在 C++ 中，字符串是字符数组的集合。
- 所以字符串以分隔符 '\0'结尾，它表示字符串的结尾。
- 所以它的大小是 2，因为 "a" 为 1 个字节，'\0' 为 1 个字节
where in case of 'a'-> it is single character. so its size would be 1-byte.
在 'a'-> 的情况下，它是单个字符。所以它的大小将是 1 字节。
char str[]="a";
or
或者
char *ptr = "c";
for 'c' -> char c = 'a';
or we can write as well
或者我们也可以写
char c = 97;
回答by ganga
'a' - 1) Character constant 2) size - 1 Character 3) Not a collection of Character array
'a' - 1) 字符常量 2) 大小 - 1 个字符 3) 不是字符数组的集合
"a" -1) String literals 2) size - 2 Character 3) collection of Character array
"a" -1) 字符串字面量 2) 大小 - 2 个字符 3) 字符数组的集合
