Cannot initialize a member subobject of type 'char ' with an lvalue of type 'const char '

Question

I have the following:

data.hpp

#include <stdio.h>
class Data{

private:
    char* input_filename;
    char* csv_filename;

public:
    Data(const char* in_filename,const char* out_csv="output.csv");
};

#endif /* data_hpp */

And data.cpp

#include "data.hpp"

Data::Data(const char* in_filename,const char* out_csv): input_filename(in_filename), output_csv(out_csv)
{}

I get the error:

Cannot initialize a member subobject of type 'char *' with an lvalue of type 'const char *'

How can I initialize two array of chars that are passed in the constructor?

Those aren't "arrays of chars", they're "pointers to chars". Two completely different things. Just make your member pointers `const` too. — Mark Ransom, Jun 04 '20 at 20:41
Change `char* input_filename;` to `std::string input_filename;`. Same for `csv_filename`. — Eljay, Jun 04 '20 at 20:42
@VictorSanchez The member you want to initialize is `csv_filename`, not `output_csv`. The compiler is right to complain (even if in a pretty roundabout way) that it doesn't understand what you are trying to call/initialize. — jvd, Jun 04 '20 at 20:48
@jvd I have to believe that's a typo, because the error message would be different. — Mark Ransom, Jun 04 '20 at 21:26
Very similar [question](https://stackoverflow.com/questions/48759558/a-value-of-type-const-char-cannot-be-used-to-initialize-an-entity-of-type-ch) - same problem, different error message. — 1201ProgramAlarm, Jun 04 '20 at 22:41

score 3 · Answer 1 · answered Jun 04 '20 at 22:32

char* is a "pointer to a non-const char".

const char* is a "pointer to a const char".

You can't assign a const char* to a char*, which is what the compiler is complaining about. So, you will have to either:

change the char* members to const char*:

class Data{

private:
    const char* input_filename;
    const char* csv_filename;

public:
    Data(const char* in_filename, const char* out_csv = "output.csv");
};

#include "data.hpp"

Data::Data(const char* in_filename, const char* out_csv):
    input_filename(in_filename), csv_filename(out_csv)
{}

change the char* members to std::string:

#include <string>

class Data{

private:
    std::string input_filename;
    std::string csv_filename;

public:
    Data(const char* in_filename, const char* out_csv = "output.csv");

    /* you can optionally change the constructor parameters to std::string, too...
    Data(const std::string &in_filename, const std::string &out_csv = "output.csv");
    */
};

#include "data.hpp"

Data::Data(const char* in_filename, const char* out_csv):
    input_filename(in_filename), csv_filename(out_csv)
{}

/* or:
Data::Data(const std::string &in_filename, const std::string &out_csv):
    input_filename(in_filename), csv_filename(out_csv)
{}
*/

Cannot initialize a member subobject of type 'char *' with an lvalue of type 'const char *'

1 Answers1

Cannot initialize a member subobject of type 'char ' with an lvalue of type 'const char '