更新：进行了一些更改并使用了strcmp

Question

我不太确定为什么大字符串（＆＃34; cat＆＃34;和＃34; dog＆＃34;）的答案不一致。我正在使用链接列表和模板的使用做一些事情。我的好奇心让我修改了模板和函数重载。如果有人能解释发生了什么，我将不胜感激。谢谢。

Function Overloading
larger(15, 27)            =  27
larger('X', 'P')          =  X
larger(4.9, 3.2)          =  4.9
larger(cat, dog)          =  dog

Using the function template to find the larger of two items
anyLarger(15, 27)         =  27
anyLarger('X', 'P')       =  X
anyLarger(4.9, 3.2)       =  4.9
anyLarger(cat, dog)       =  cat

Compare two strings:   cat, dog
cat is greater than dog

string strCat = cat
string strDog = dog
strDog is greater than strCat

这是运行程序后的结果。

#include <iostream>
#include <string.h>
using namespace std;

// Function overloading and the use of templates


// overloading the function larger
int larger(int, int);
char larger(char, char);
double larger(double, double);
string larger(string, string);


template <class elementType>
elementType anyLarger(elementType parameter1, elementType parameter2);


int main(){

  cout << endl;
  cout << "// Function Overloading" << endl;


  cout << "larger(15, 27)              =  " << larger(15, 27) << endl;
  cout << "larger('X', 'P')            =  " << larger('X', 'P') << endl;
  cout << "larger(4.9, 3.2)            =  " << larger(4.9, 3.2) << endl;
  cout << "larger(\"cat\", \"dog\")        =  " << larger("cat", "dog") << endl;

  cout << endl;
  cout << "// Using the function template to find the larger of two items" << endl;
  cout << "anyLarger(15, 27)           =  " << anyLarger(15, 27) << endl;
  cout << "anyLarger('X', 'P')         =  " << anyLarger('X', 'P') << endl;
  cout << "anyLarger(4.9, 3.2)         =  " << anyLarger(4.9, 3.2) << endl;
  cout << "anyLarger(\"cat\", \"dog\")     =  " << anyLarger("cat", "dog") << endl;
  cout << endl;


  cout << "// Compare two strings using >= :   \"cat\", \"dog\"" << endl;
  if ("cat" >= "dog") {
    cout << "\"cat\" is greater than \"dog\"" << endl;
  }
  else {
    cout << "\"dog\" is greater than \"cat\"" << endl;
  }

  cout << endl;
  cout << "// The use of variables: strCat and strDog. Compare using >=" << endl;
  string strCat = "cat";
  string strDog = "dog";
  cout << "string strCat = \"cat\";" << endl;
  cout << "string strDog = \"dog\";" << endl;
  if (strCat >= strDog) {
    cout << "strCat is greater than strDog" << endl;
  }
  else {
    cout << "strDog is greater than strCat" << endl;
  }
  cout << endl;


  cout << "// Using strcmp.   strcmp(\"cat\", \"dog\")" << endl; 
  int result = strcmp("cat", "dog");
  if (result > 0) {
    cout << "\"cat\" is greater than \"dog\"" << endl;
  }
  else {
    cout << "\"dog\" is greater than \"cat\"" << endl;
  }
}

// Overloading larger
int larger(int x, int y) {
if (x >= y)
    return x;
  else 
    return y;
}


char larger(char a, char b) {
  if (a >= b)
    return a;
  else 
    return b;
}


double larger(double p, double q) {
  if (p >= q)
    return p;
  else
    return q;
}

string larger(string y, string z) {
  if (y >= z)
    return y;
  else
    return z;
}


// Defining the template function
template <class elementType>
elementType anyLarger(elementType parameter1, elementType parameter2)
{
  if (parameter1 >= parameter2)
    return parameter1; 
  else
    return parameter2;
}

============================================== < / p>

更新：进行了一些更改并使用了strcmp

// Function Overloading
larger(15, 27)              =  27
larger('X', 'P')            =  X
larger(4.9, 3.2)            =  4.9
larger("cat", "dog")        =  dog

// Using the function template to find the larger of two items
anyLarger(15, 27)           =  27
anyLarger('X', 'P')         =  X
anyLarger(4.9, 3.2)         =  4.9
anyLarger("cat", "dog")     =  cat

// Compare two strings using >= :   "cat", "dog"
"cat" is greater than "dog"

// The use of variables: strCat and strDog. Compare using >=
string strCat = "cat";
string strDog = "dog";
strDog is greater than strCat

// Using strcmp.   strcmp("cat", "dog")
"dog" is greater than "cat"

=====

更新：输出

border-radius

Answer 1

在两种情况下，你都没有按字典顺序比较字符串。

"cat" >= "dog"

这是比较char指针，因为文字"cat"和"dog"的类型是const char*。它可以给出任何结果，具体取决于编译器决定如何实现文字。

要按字典顺序比较C风格的字符串（包括这些字符串），必须使用函数strcmp。

strCat >= strDog

这是按字典顺序比较字符串，因为std::string提供了明确实现此类比较的比较运算符。

Answer 2

"cat" >= "dog"

您正在比较指针而不是实际值。使用strcmp。

Answer 3

这是因为字符串文字（例如"cat"）不属于std::string类型。您正在对两个不相关的const char数组进行指针比较。

Answer 4

当您比较它们时，文字字符串"cat"和"dog"实际上是指针到字符数组，所以最大的将是恰好存储的字符串在更高的位置记忆。

您的string larger(string y, string z)有效，因为std::string可以由char*构建，因此"cat"和"dog"会被转换为std::string个对象。比较。

另一方面，模板函数将它们作为实际类型接受，当它们作为参数传递时，变为const char*并且仅对它们的地址进行比较。

Answer 5

正如其他人已经提到的那样，在你的行中

cout << "anyLarger(cat, dog)       =  " << anyLarger("cat", "dog") << endl;

您正在调用anyLarger<const char &[]>，即您使用字符串文字参数调用anyLarger，这实际上归结为比较指针而不是字符串。您可以通过以下行之一使用std :: string参数调用函数来解决此问题：

larger("cat", "dog");
anyLarger<std::string>("cat", "dog");
anyLarger(std::string("cat"), std::string("dog"));
anyLarger("cat"s, "dog"s); // C++14

或者您可以为字符串文字（或任何C类型的字符串，无论您选择什么）进行模板特化：

template <>
elementType anyLarger<char*>(char* parameter1, char* parameter2)
{
    if (strcmp(parameter1, parameter2) >= 0)
      return parameter1; 
    else
      return parameter2;
}

C ++字符串。为什么答案显示字符串＆＃34; dog＆＃34;大于＆＃34; cat＆＃34;，然后＆＃34; cat＆＃34;大于＆＃34;狗＆＃34;？

更新：进行了一些更改并使用了strcmp

更新：输出

5 个答案: