C++ 不推荐从字符串文字转换为 char*
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/13690306/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Conversion from string literal to char* is deprecated
提问by Andrew T
I keep getting the error "Conversion from string literal to char* is deprecated" in my code. The purpose of the code is to use a pointer-to-pointer to assign string1 and string2 a word, then print it out. How can I fix this?
我在我的代码中不断收到错误“不推荐使用从字符串文字到 char* 的转换”。代码的目的是使用一个指向指针的指针给 string1 和 string2 分配一个单词，然后打印出来。我怎样才能解决这个问题？
Here is my code:
这是我的代码：
#include <iostream>
using namespace std;
struct WORDBLOCK
{
char* string1;
char* string2;
};
void f3()
{
WORDBLOCK word;
word.string1 = "Test1";
word.string2 = "Test2";
char *test1 = word.string1;
char *test2 = word.string2;
char** teststrings;
teststrings = &test1;
*teststrings = test2;
cout << "The first string is: "
<< teststrings
<< " and your second string is: "
<< *teststrings
<< endl;
}
回答by Keith Thompson
C++ string literals are arrays of constchar, which means you can't legally modify them.
C++ 字符串文字是const数组char，这意味着您不能合法地修改它们。
If you want to safely assign a string literal to a pointer (which involves an implicit array-to-pointer conversion), you need to declare the target pointer as const char*, not just as char*.
如果要安全地将字符串文字分配给指针（这涉及隐式数组到指针的转换），则需要将目标指针声明为const char*，而不仅仅是char*。
Here's a version of your code that compiles without warnings:
这是编译时没有警告的代码版本：
#include <iostream>
using namespace std;
struct WORDBLOCK
{
const char* string1;
const char* string2;
};
void f3()
{
WORDBLOCK word;
word.string1 = "Test1";
word.string2 = "Test2";
const char *test1 = word.string1;
const char *test2 = word.string2;
const char** teststrings;
teststrings = &test1;
*teststrings = test2;
cout << "The first string is: "
<< teststrings
<< " and your second string is: "
<< *teststrings
<< endl;
}
Consider what could happen if the language didn'timpose this restriction:
考虑一下如果语言没有施加这个限制会发生什么：
#include <iostream>
int main() {
char *ptr = "some literal"; // This is invalid
*ptr = 'S';
std::cout << ptr << "\n";
}
A (non-const) char*lets you modify the data that the pointer points to. If you could assign a string literal (implicitly converted to a pointer to the first character of the string) to a plain char*, you'd be able to use that pointer to modify the string literal with no warnings from the compiler. The invalid code above, if it worked, would print
A (non- const)char*允许您修改指针指向的数据。如果您可以将一个字符串文字（隐式转换为指向字符串第一个字符的指针）分配给一个 plain char*，您将能够使用该指针修改字符串文字，而编译器不会发出警告。上面的无效代码，如果有效，将打印
Some literal
-- and it might actually do so on some systems. On my system, though, it dies with a segmentation fault because it attempts to write to read-only memory (not physical ROM, but memory that's been marked as read-only by the operating system).
- 它实际上可能会在某些系统上这样做。但是，在我的系统上，它因分段错误而死亡，因为它尝试写入只读内存（不是物理 ROM，而是被操作系统标记为只读的内存）。
(An aside: C's rules for string literals are different from C++'s rules. In C, a string literal is an array of char, notan array of const char-- but attempting to modify it has undefined behavior. This means that in C you can legally write char *s = "hello"; s[0] = 'H';, and the compiler won't necessarily complain -- but the program is likely to die with a segmentation fault when you run it. This was done to maintain backward compatibility with C code written before the constkeyword was introduced. C++ had constfrom the very beginning, so this particular compromise wasn't necessary.)
（旁白：C 的字符串文字规则与 C++ 的规则不同。在 C 中，字符串文字是 的数组char，而不是的数组const char-- 但尝试修改它具有未定义的行为。这意味着在 C 中您可以合法地编写char *s = "hello"; s[0] = 'H';, 并且编译器不一定会抱怨——但是当你运行它时，程序很可能会因分段错误而死。这样做是为了保持与const引入关键字之前编写的 C 代码的向后兼容性。C++const从一开始就有，所以这种特殊的妥协是没有必要的。）
