修改c字符串 [英] Modifying a c string

问题描述

我试图实现 tolower（char *）函数，但我遇到访问冲突错误。我知道这是因为编译器将字符串字面量存储在只读存储器中。这是真的？
以下是一些代码：

I'm trying to implement tolower(char *) function, but I get access violation error. I came to know that this is because to compiler stores string literals in a read-only memory. Is this true? Here's some code:

char* strToLower(char *str)
{
    if(str == nullptr)
        return nullptr;

    size_t len = strlen(str);
    if(len <= 0)
        return nullptr;

    for(size_t i = 0; i < len; i++)
        *(str+i) = (char)tolower(*(str+i));//access violation error

    return str;
}

int main()
{
    char *str = "ThIs Is A StRiNgGGG";

    cout << strToLower(str) << endl;

    system("pause");
    return 0;
}

如果这是真的，我应该如何实现这样的功能？ p>

If this is true, how am I supposed to implement such function?

推荐答案

是的，这是真的。您不能修改字符串文字。事实上，如果你的编译器不是从1922年，它将阻止你甚至获得一个非 - const 指向一个字符串字面量的第一位。

Yes, it's true. You cannot modify a string literal. In fact, if your compiler were not from 1922 it would have prevented you from even obtaining a non-const pointer to a string literal in the first place.

你没有说明你的目标，所以当你问我应该如何实现这样的功能时，你不清楚你想要做什么。但您可以对字符串文字进行复制，以获取您自己的字符串，然后按照以下步骤进行修改：

You didn't state your goals, so when you ask "how am I supposed to implement such function" it's not really clear what you want to do. But you can make a copy of the string literal to get your own string, then modify that as you please:

// Initialises an array that belongs to you, by copying from a string literal
char str[] = "ThIs Is A StRiNgGGG";

// Obtains a pointer to a string literal; you may not modify the data it points to
const char* str = "ThIs Is A StRiNgGGG";

// Ancient syntax; not even legal any more, because it leads to bugs like yours
char* str = "ThIs Is A StRiNgGGG";

当然，由于这是C ++，你不应该首先使用C字符串：

Of course, since this is C++, you should not be using C-strings in the first place:

std::string str("ThIs Is A StRiNgGGG");

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