Convert a string from uppercase letters to lowercase letters

709. Convert to lowercase letters

Easy difficulty 140 Favorites and sharing switch to English to receive dynamic feedback

Implement the function ToLowerCase(), which receives a string parameter str, converts the uppercase letters in the string to lowercase letters, and then returns the new string.

 

Example 1:

Input: "Hello"
 Output: "hello"

Example 2:

Input: "here"
 Output: "here"

Example  3:

Input: "LOVELY"
 Output: "lovely"

Number of passes: 59,537 Number of submissions: 78,268

This question is actually not difficult at all. There are many methods. I chose to use API, tanform():

string rets=str;

 transform(rets.begin(),rets.end(),rets.begin(),tolower); 

Then an error occurred. . . no matching function for call to 'transform' . . .

According to experience, the function does exist, but the parameter types should not match.

Thanks https://blog.csdn.net/u011089523/article/details/48499023?ops_request_misc=&request_id=&biz_id=102&utm_term=mo%2520match%2520function%2520for%2520call%2520to%2520&utm_medium=distribute.pc_search_result .none-task-blog -2~all~sobaiduweb~default-1-48499023.pc_search_result_no_baidu_js

Three workarounds are provided:

1. Because there are implemented functions (rather than macros) in the global namespace, we namespace explicitly, which doesn't always work, but works fine in my g++ environment:

transform(str.begin(), str.end(), str.begin(), ::toupper);

•  

2. Write a function yourself—wrapper

inline char charToUpper(char c)
{
    return std::toupper(c);
}

3. Force conversion: Convert toupper into a function pointer with a return value of int and only one int parameter.

transform(str.begin(), str.end(), str.begin(), (int (*)(int))toupper);

The third method is used here: if you can pass the questions correctly:

class Solution {
public:
    string toLowerCase(string str) {
        string rets=str;
        transform(rets.begin(),rets.end(),rets.begin(),(int (*)(int))tolower); 
        return rets;
    }
};

The first one is also possible, personal test: transform(rets.begin(),rets.end(),rets.begin(),::tolower);