error: cannot convert 'std::cxx11::string' {aka 'std::cxx11::basic_string<char>'} to 'const char*' line 23

Question

I was comparing two strings, but unfortunately this error occurred

error: cannot convert 'std::__cxx11::string' {aka 'std::__cxx11::basic_string<char>'} to 'const char*' line 23

#include <iostream>
#include <string.h>

using namespace std;

class car {

    public:
    int feulcp, batterycp, length, height, width, seater, torque, power, temp;
    char ownername[20], noplate[12], statecheck[20];

    string statename[28] = {"andhra pradesh", "arunachal pradesh", "assam,bihar", "chhattisgarh", "goa", "gujarat", "haryana", "himachal pradesh", "jharkhand", "karnataka", "kerala", "madhya pradesh", "maharashtra", "manipur", "meghalaya", "mizoram", "nagaland", "odisha", "punjab", "rajasthan", "sikkim", "tamil nadu", "telangana", "tripura", "uttarakhand", "uttar pradesh", "west bengal"};

    car() {
        cout << "Please Enter Your State Name: ";
        y:
        cin >> statecheck;
        for(int i=0; i<=27; i++) {
            temp = strcmp(statename[i], statecheck); // Here is the error!!!
            if(temp == 0) {
                goto x;
            }
            else
                cout << "INVALID STATE NAME \n PLEASE RE-ENTER ";
            goto y;
        }
        x:
            cout << "successful";
    }

};

int main() {
    car car1;
    return 0;
}

You can use the c_str() member function of std::string to get a char* that is usable by strcmp. But there are other issues in your code (probably typos) - please try to tidy up your post. — Adrian Mole
– Adrian Mole, Commented Aug 28, 2021 at 15:06
OK, apart from the fact that there is seldom a reason to use goto statements in C++, ask yourself what happens if the entered state text does not match the very first in the list. How will your code ever test it against the second in the list? Or the third? — Adrian Mole
– Adrian Mole, Commented Aug 28, 2021 at 15:14
Also, until such time as you #include <string>, there is no std::string formally dictated. If you're using the std::string class, you must include <string> . There are no exceptions, and if it appears to work, that just means you rolled the dice and you auto tires didn't flatten. — WhozCraig
– WhozCraig, Commented Aug 28, 2021 at 15:18

Remy Lebeau · Accepted Answer · 2021-08-28 18:58:48Z

1

strcmp() takes const char* parameters, but you are passing it a std::string object instead, hence the error. Use the std::string::c_str() method to get a const char*:

temp = strcmp(statename[i].c_str(), statecheck);

That being said, there is no need to use strcmp() at all, as std::string has its own operator== and compare() methods for performing string comparisons, eg:

if (statename[i] == statecheck){

if (statename[i].compare(statecheck) == 0){

edited Aug 28, 2021 at 18:58

answered Aug 28, 2021 at 18:53

Remy Lebeau

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Comments

Peter Mortensen · Accepted Answer · 2023-11-14 16:14:30Z

0

Synopsis: strcmp()

int strcmp(const char *s1, const char *s2);

Both arguments for strcmp() should be interpreted as type unsigned char, and their difference is calculated.

temp=strcmp(statename[i],statecheck);

In your code, "statename" is "std::string" and the compiler fails the implicit conversion from std::string to const char*.

Solution

temp = strcmp(statename[i].c_str(), statecheck);

std::string::c_str: will represent the current value of the string in C-string.

Note

Replacing:

char statecheck[20]; with std::string statecheck; temp=strcmp(statename[i].c_str(),statecheck); and if(temp==0) with if(statename[i] == statecheck)

will be better and, as Adrian Mole explained, the code will fail to provide the expected result.

edited Nov 14, 2023 at 16:14

Peter Mortensen

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answered Feb 18, 2022 at 20:43

Vipin Chandran

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