用非常量函数参数初始化数组 [英] Initialize array with a non-const function argument

问题描述

有没有办法用非常量整数初始化数组，或者使现有变量恒定以使其成为有效参数?

Is there any way to initialize an array with a non-const integer, or to make the existing variable constant in order to make it a valid argument?

bool f( const char s[], const int n )
{
    char c[n]; // error: expression must have a constant value
}

推荐答案

否，一般情况下不行.改为使用vector<char> c(n).

No, not in the general case. Use vector<char> c(n) instead.

简化的，几乎正确的解释:如果在编译时不知道n是什么，则编译器也不会.因此，它无法为阵列预留内存.这就是vector存在的原因.

Simplified, almost correct explanation: if you don't know what n is at compile time, neither does the compiler. So it cannot put aside memory for the array. This is why vector exists.

如果您在其他地方需要它，可以始终使用&c[0]来获取指向char的指针.

You can always use &c[0] to get the pointer to char if you need it elsewhere.

但是在C99中是可能的，显然.感谢 @Matt McNabb 指出这一点.如果您可以等待几年，您也许也可以在C ++中对其进行编译.同时，使用vector.

But it is possible in C99, apparently. Thanks to @Matt McNabb for pointing this out. If you can wait a few years you might be able to compile it in C++, too. In the meanwhile, use vector.

如果您坚持在C ++中使用数组"，则必须执行以下操作:

If you insist to have an "array" in C++, you would have to do something like:

char* c = new char[n];

如果您的程序不能永远运行或执行得太频繁，您甚至可以直接保留它，而不必费心删除.不过，像Valgrind这样的工具可能会抱怨.

If your program does not run forever, or do this too often, you can even just leave it as it is and not bother deleting. Tools like Valgrind might complain though.

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