字符串数组到C ++函数 [英] String array to C++ function

问题描述

我想检查一个给定的名称是否在可能的名称数组内.我写了这个小的调试函数(是的，我知道它总是返回true)，试图理解为什么它不起作用以及为什么出现以下错误.

I want to check if a given name is inside an array of possible names. I wrote this small debugging function ( yeah... I know it always return true ) trying to understand why it does not work and why I get the below error.

char[] people_names = ["Mario","Luigi"];

bool lookupTerm (string term, string possible_names[]){
   for(const string &possible_name : possible_names)
     cout << possible_name <<  endl;

    return true;
}

错误

jdoodle.cpp: In function 'bool lookupTerm(std::__cxx11::string, std::__cxx11::string*)':
jdoodle.cpp:19:38: error: no matching function for call to 'begin(std::__cxx11::basic_string<char>*&)'

我知道它必须确实很明显，但是根据我的搜索，它应该可以工作.有人可以指出我正确的方向吗?

I know that it must be really obvious but according to what I have searched for, it should work. Can someone point me in the right direction?

推荐答案

问题是，当您将数组传递给函数时，它会衰减为指向其第一个元素的指针.

The problem is that when you pass an array to a function, it decays to a pointer to its first element.

尝试将参数声明为数组并不重要，编译器仍会将其转换为指针.声明参数时，string possible_names[]等于string* possible_names.

It doesn't matter if you attempt to declare the argument as an array, the compiler still translates it as a pointer. string possible_names[] is equal to string* possible_names when you declare arguments.

简单的解决方案是使用 std::vector 或 std::array ，具体取决于您的需求和用例.

The simple solution is to use either std::vector or std::array depending on your needs and use-case.

使用std::vector您的代码应如下所示:

Using std::vector your code would look something like this:

std::vector<std::string> people_names = { "Mario", "Luigi" };

bool lookupTerm(const std::string& term, const std::vector<std::string>& possible_names) {
    for (const std::string &possible_name : possible_names)
    {
        if (possible_name == term)
            return true;
    }
    return false;
}

使用 std::find :

bool lookupTerm(const std::string& term, const std::vector<std::string>& possible_names) {
    return std::find(possible_names.begin(), possible_names.end(), term) != possible_names.end();
}

如果性能成为问题，则可以使用排序向量(使用 std::lower_bound :

If performance becomes a problem you can increase the performance of this by using a sorted vector (using std::sort) and std::lower_bound:

//at one point:
std::sort(people_names.begin(), people_names.end());

bool lookupTerm(const std::string& term, const std::vector<std::string>& sorted_possible_names) {
    //sorted_possible_names must be always sorted when you call this!
    auto i = std::lower_bound(sorted_possible_names.begin(), sorted_possible_names.end(), term);
    return (i != sorted_possible_names.end() && *i == term);
}

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