I'm trying to solve this issue E0144 a value of type "const char *" cannot be used to initialize an entity of type "char *"

It does compile on different compilers but it gives me errors on visual studio 2019 it doesn't compile

Errors C2440 'initializing': cannot convert from 'const char [9]' to 'char *' E0144 a value of type "const char *" cannot be used to initialize an entity of type "char *"

I tried solving the issue but can't seem to understand it.

#include<iostream>
#include<cstring>


using namespace std;

int processString(char* string) {
    int vowels = 0;
    bool a = false, e = false, i = false, o = false, u = false;


    for (int k = 0; k < strlen(string); k  ) {
        switch (string[k]) {
        case 'a':case 'A': a = true; break;
        case 'e':case 'E': e = true; break;
        case 'i':case 'I': i = true; break;
        case 'o':case 'O': o = true; break;
        case 'p':case 'U': u = true; break;
        }
    }
    vowels  = a ? 1 : 0;
    vowels  = e ? 1 : 0;
    vowels  = i ? 1 : 0;
    vowels  = o ? 1 : 0;
    vowels  = u ? 1 : 0;


    return vowels; // the number of vowels in string
}

int main() {

    char* sports[] = { "football","basketball","golf","cricket","Chess","badminton" };
    int vowels;
    for (int j = 0; j < 6; j  ) {

        vowels = processString(sports[j]);
        cout << "String \'" << sports[j] << "\' contains \'" << vowels << "\' vowels.\n";
    }
}

CodePudding user response：

The line

char* sports[] = { "football","basketball","golf","cricket","Chess","badminton" };

is valid in C, but not in C . In C , pointers to string literals must be of type const char *.

Therefore, you should change the line to the following:

const char* sports[] = { "football","basketball","golf","cricket","Chess","badminton" };

If you want to pass a pointer to a string literal to the function processString, then you should also change the parameter of that function from char * to const char *.

CodePudding user response：

I suggest to use strdup() (or simply std::string). As the compiler suggests, "football" et. al. are const char* and a const cannot be used to initialize a non-const.

CodePudding user response：

According to the C 17 Standard (5.13.5 String literals)

8 Ordinary string literals and UTF-8 string literals are also referred to as narrow string literals. A narrow string literal has type “array of n const char”, where n is the size of the string as defined below, and has static storage duration (6.7)

So you have to write

const char* sports[] = { "football","basketball","golf","cricket","Chess","badminton" };

This for loop uses a magic number 6.

for (int j = 0; j < 6; j  ) {

    vowels = processString(sports[j]);
    cout << "String \'" << sports[j] << "\' contains \'" << vowels << "\' vowels.\n";
}

Using magic numbers is error prone. Instead you could use a range-based for loop like

for ( const auto &s : sports ) {

    size_t vowels = processString( s );
    cout << "String \'" << s << "\' contains " << vowels << " vowels.\n";
}

The parameter of the function processString correspondingly must also have the qualifier const .

Moreover the function contains a bug because the boolean values are not reset to false within the for loop.

Using your approach the function can be declared and defined the following way

size_t processString( const char* s ) {
    size_t vowels = 0;

    for ( ; *s;   s ) {
        bool a = false, e = false, i = false, o = false, u = false;

        switch ( *s ) {
        case 'a':case 'A': a = true; break;
        case 'e':case 'E': e = true; break;
        case 'i':case 'I': i = true; break;
        case 'o':case 'O': o = true; break;
        case 'p':case 'U': u = true; break;
        }

        vowels  = a ? 1 : 0;
        vowels  = e ? 1 : 0;
        vowels  = i ? 1 : 0;
        vowels  = o ? 1 : 0;
        vowels  = u ? 1 : 0;
    }

    return vowels; // the number of vowels in string
}