字符串常量在C ++中可以生存多长时间? [英] How long does a string constant live in c++?

问题描述

我一直想知道，字符串常量在C ++中可以生存多长时间.例如，如果我在函数内创建一些const char * str ="something"，返回str的值是否安全?

I've been wondering, how long does a string constant live in C++. For example, if I create some const char *str = "something" inside a function, would it be safe to return the value of str?

我编写了一个示例程序，很惊讶地看到这样的返回值仍然存储了该字符串.这是代码:

I wrote a sample program and was really surprised to see that such returned value still stored that string. Here is the code:

#include <iostream>
using namespace std;

const char *func1()
{
    const char *c = "I am a string too";
    return c;
}

void func2(const char *c = "I'm a default string")
{
    cout << c << endl;
}

const int *func3()
{
    const int &b = 10;
    return &b;
}

int main()
{
    const char *c = "I'm a string";
    cout << c << endl;
    cout << func1() << endl;
    func2();
    func2("I'm not a default string");
    cout << *func3() << endl;
    return 0;
}

它给了我以下输出:

我是一个字符串

I'm a string

我也是一个字符串

我是默认字符串

我不是默认字符串

10

func3只是在查找是否可以与其他类型一起使用.
所以问题是:返回指向在该函数内创建的字符串常量的指针是否安全(如func1()一样)?
另外，使用func2()中的默认字符串值是否安全?

The func3 is there just to find out if the same works with other types.
So the question is: is it safe to return a pointer to a string constant created within that function (as in func1())?
Also, is it safe to use the default string value as in func2()?

推荐答案

字符串文字具有静态存储持续时间，并且可以延长程序的寿命.从草稿C ++标准部分2.14.5 字符串文字段落 8 说(强调我的前进):

A string literal has static storage duration and lasts the life of the program. From the draft C++ standard section 2.14.5 String literals paragraph 8 which says (emphasis mine going forward):

还引用了普通字符串文字和UTF-8字符串文字 作为狭窄的字符串文字.窄字符串文字的类型为数组 n const char"，其中n是如下定义的字符串的大小， 并且具有静态存储期限(3.7).

Ordinary string literals and UTF-8 string literals are also referred to as narrow string literals. A narrow string literal has type "array of n const char", where n is the size of the string as defined below, and has static storage duration (3.7).

以及3.7.1 静态存储期限第 1 段:

所有没有动态存储持续时间的变量，没有 线程存储的持续时间，并且不是本地的都有静态存储 期间. 这些实体的存储期限为持续时间 程序(3.6.2，3.6.3).

All variables which do not have dynamic storage duration, do not have thread storage duration, and are not local have static storage duration. The storage for these entities shall last for the duration of the program (3.6.2, 3.6.3).

另一方面，func3中的第二种情况无效.引用的临时绑定的生存期在该引用的生存期内一直存在，在这种情况下，函数返回时将终止该生存期. 12.2部分对此进行了说明:

The second case in func3 on the other other hand is not valid. The lifetime of a temporary bound to a reference persists for the life of the reference, which in this case ends when the function returns. This is covered in section 12.2 which says:

第二种情况是引用绑定到临时目录. ¹¹⁵ 引用绑定到的临时对象或引用的临时对象 引用绑定到的子对象的完整对象 在参考的有效期内持续存在，除了:

The second context is when a reference is bound to a temporary.¹¹⁵ The temporary to which the reference is bound or the temporary that is the complete object of a subobject to which the reference is bound persists for the lifetime of the reference except:

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