How to use char* as a key in std:: map

Although syntactically valid, using char* as the key for std::map is not recommended. The primary reason is that std::map defaults to using std::less for key comparison, which compares char* keys based on their memory addresses rather than the string content they point to. This is typically not the desired behavior, as different char* variables pointing to the same string content may reside at different memory addresses, causing std::map to incorrectly search and sort key-value pairs based on string content.

For example, consider the following code snippet:

cpp
#include <map>
#include <iostream>

int main() {
    std::map<char*, int> myMap;

    char* key1 = "key";
    char* key2 = "key";

    myMap[key1] = 100;
    myMap[key2] = 200;

    std::cout << "Number of elements: " << myMap.size() << std::endl;  // Output: 2
    std::cout << "Value at key1: " << myMap[key1] << std::endl;        // Output: 100
    std::cout << "Value at key2: " << myMap[key2] << std::endl;        // Output: 200
}

In this example, even though key1 and key2 point to the same string content, they may be stored at different memory addresses. Therefore, myMap treats them as distinct keys and creates two separate key-value pairs.

To resolve this issue, the recommended approach is to use std::string as the key type. std::string objects in std::map are compared based on their actual content, which is typically the desired behavior. This avoids problems caused by differing pointer addresses. Here is the modified code:

cpp
#include <map>
#include <iostream>
#include <string>

int main() {
    std::map<std::string, int> myMap;

    std::string key1 = "key";
    std::string key2 = "key";

    myMap[key1] = 100;
    myMap[key2] = 200;

    std::cout << "Number of elements: " << myMap.size() << std::endl;  // Output: 1
    std::cout << "Value at key: " << myMap[key1] << std::endl;         // Output: 200
}

In this modified example, myMap correctly treats key1 and key2 as the same key and stores only one key-value pair. This approach is safer and more logical.