函数中不接受c++参数

Question

我的c++程序是这样的：

#include <iostream>
#include <cstdlib>
#include <dos.h>
using namespace std;

void arr(int pts,string *splt_msg){
  for(int x=-1;x<pts-1;x++){
    string input;
    cout<<"Enter part "<<x<<endl;
    cin>>input;
    (*splt_msg)[x]=input;
  }
}

void print_arr(string *splt_msg,int del,int parts){
  for(int x=-1;x<parts-1;x++){
    cout<<(*splt_msg)[x];
    delay(del);
  }
}

int main(){
  cout<<"Parts in message: ";
  int parts;
  cin>>parts;
  cout<<"Delay between parts(ms): ";
  int del;
  cin>>del;
  parts--;
  string splt_msg[parts];
  string (*Parr)[parts]=&splt_msg;
  arr(parts,Parr);
  print_arr(Parr,del,parts);
  return 0;
}

以下是错误代码(在windows和mingw上)：

c:\Users\User\Desktop\c++>g++ -o program test1.cpp
In file included from test1.cpp:3:0:
c:\mingw\include\dos.h:54:2: warning: #warning "<dos.h> is obsolete; consider using <direct.h> instead." [-Wcpp]
  ^~~~~~~
test1.cpp: In function 'void arr(int, std::__cxx11::string*)':
test1.cpp:18:14: error: 'delay' was not declared in this scope
delay(del);
        ^
test1.cpp: In function 'int main()':
test1.cpp:32:17: error: cannot convert 'std::__cxx11::string (*)[parts] {aka std::__cxx11::basic_string<char> (*)[parts]}' to 'std::__cxx11::string* {aka std::__cxx11::basic_string<char>*}' for argument '2' to 'void arr(int, std::__cxx11::string*)'
   arr(parts,Parr);
                 ^
test1.cpp:33:27: error: cannot convert 'std::__cxx11::string (*)[parts] {aka std::__cxx11::basic_string<char> (*)[parts]}' to 'std::__cxx11::string* {aka std::__cxx11::basic_string<char>*}' for argument '1' to 'void print_arr(std::__cxx11::string*, int, int)'
   print_arr(Parr,del,parts);
                           ^

有没有人知道我做错了什么和解决办法？谢谢你的帮助，我只是想写一个简单的程序来测试一些概念，比如将指针传递给函数，但它似乎不起作用。

Answer 1

这段代码更像是C语言风格，而不是C++。你正在做一些容易出错的困难的事情。试着使用向量之类的

string splt_msg[parts];

甚至不应该求值，因为parts不是常量表达式。

尝试使用std::vector之类的东西。并通过引用传递。例如：

#include <iostream>
#include <string>
#include <vector>
#include <Windows.h>

template<typename T>
T Read() noexcept {
    T output{};
    std::cin >> output;
    return output;
}

void arr(std::vector<std::string>& splt_msg) {
    for (auto& msg : splt_msg) {
        std::cout << "Enter part \n";
        std::cin >> msg;
    }
}

void print_arr(std::vector<std::string> const& splt_msg, int delay) {
    for (auto& msg : splt_msg) {
        std::cout << msg;
        Sleep(delay);
    }
}

int main() {
    std::cout << "Parts in message: ";
    auto parts = Read<int>();

    std::cout << "Delay between parts(ms): ";
    auto delay = Read<int>();

    std::vector<std::string> splt_msg(parts);
    arr(splt_msg);
    print_arr(splt_msg, delay);
}

编辑:或者更好:使用对象

#include <iostream>
#include <string>
#include <vector>
#include <Windows.h>

template<typename T>
T Read() noexcept {
    T output{};
    std::cin >> output;
    return output;
}

class SplitMessage {
private:
    std::vector<std::string> splitMessage;
public:
    SplitMessage(size_t length) noexcept : splitMessage(length) {}

    void GetData() noexcept;
    void PrintData(int delay) const noexcept;
};

void SplitMessage::GetData() noexcept {
    for (auto& msg : splitMessage) {
        std::cout << "Enter part \n";
        std::cin >> msg;
    }
}

void SplitMessage::PrintData(int delay) const noexcept {
    for (auto& msg : splitMessage) {
        std::cout << msg;
        Sleep(delay);
    }
}

int main() {
    std::cout << "Parts in message: ";
    auto parts = Read<int>();

    std::cout << "Delay between parts(ms): ";
    auto delay = Read<int>();

    SplitMessage splt_msg(parts);
    splt_msg.GetData();
    splt_msg.PrintData(delay);
}

Answer 2

这两个函数都需要一个std::string* (指向字符串的指针)作为第一个参数，但两次都需要传递std::string*[] (指向字符串的指针数组)作为第一个参数。解决方案取决于您想要实现什么，但我猜，您希望使用索引器为数组的一个元素调用函数：print_arr(Parr[0],del,parts);

其他一些注意事项：

• for(int x=-1;x<parts-1;x++){cout<<(*splt_msg)[x];...}将访问字符串的第-1个字符，即UB，但可能会崩溃。for(int x=0;x<parts;x++)
• string splt_msg[parts];不是有效的C++，因为parts在编译时不是常量。