无法将字符串转换为const char

Question

I have this function and the compiler yells at me saying "Cannot convert string to const char".

void 
DramaticLetters(string s, short TimeLength)
{
    for(int i = 0, sLen = strlen(s); i < sLen; i++){
        cout << s[i];
        Sleep(TimeLength);
    }
}

There's something wrong with the strlen, I think

Answer 1

strlen() is for C const char* strings. To get the length of a string s , use s.size() or s.length() . If you want to get a C string from a string , use s.c_str() .

Although C++ makes it seem that const char* and string are interchangeable, that only goes one way when converting const char* to string .

There is no reason why you would want to use strlen either. strlen is most likely defined with a loop, which will never be as efficiant as size() , which is most likley just a getter for a length property of the string class. Only convert string to C strings when calling C functions for which there is not a C++ alternative.

Answer 2

You should not mix C and C++ string functions. Instead of strlen() (a C-style function), use string::size() :

for(int i = 0, sLen = s.size(); i < sLen; i++) {
    cout << s[i];
    Sleep(TimeLength);
}

Here you have a reference with all methods from class string .

Answer 3

As chris said in his comment, strlen is used for a const char * , whereas you're passing it a string . Instead of

for(int i = 0, sLen = strlen(s); i < sLen; i++){
    cout << s[i];
    Sleep(TimeLength);
}

Use this:

for(int i = 0, sLen = s.length(); i < sLen; i++){
    cout << s[i];
    Sleep(TimeLength);
}

Answer 4

strlen operates on char const * . If you really wanted to, you could do strlen(s.c_str()) , but std::string has a lot of functionality, including a length() method, which returns the number of characters in the string

Answer 5

Few remarks:

• You do not modify the string within the function so better pass a const reference to it(const string& s)

• The string itself defines methods for getting its length - s.size() and s.length() both will work. Additional benefit is both this methods are constant with respect to complexity as opposed to the linear complexity of strlen

• If you REALLY want to use strlen use s.c_str(): strlen(s.c_str())