Why I can not initialize the char array in the structure

Question

I tried to initialize the char array in the structure declaration as follows. But he could not compile the error message. Please let me know why it cannot be compiled.

#include <iostream>

struct A {
    const char value_in_struct[] = "a";  // this line gives me a error message.
};

void t(void) {
    const char value[] = "a";  // this line was ok at compiling
    std::cout << "value = " << value << std::endl;
}

I got the following error message from gcc.

../static_constexpr_array.hpp:16:33: error: initializer-string for array of chars is too long [-fpermissive]
  const char value_in_struct[] = "a";
                                 ^

Thanks, using the time for me.

Answer 1

The problem is that the size of the array cannot be deduced automatically from the initializer in the class. The error message generated by clang is perfectly clear (see here ):

prog.cc:4:34: error: array bound cannot be deduced from an in-class initializer
    const char value_in_struct[] = "a"; 
                                 ^

? . , , - ? , (. ):

A a = {"abc"};

, .

(. ).

#include <iostream>

struct A {
    const char value_in_struct[2] = "a";  
};

void t(void) {
    char value[] = "a";
    std::cout << "value = " << value << std::endl;
}

Answer 2

, const char var [] = "something"; , var char , . . 10.

, , .. .

A, const char [], , , . , - , const, , .

, struct - type char * , , .

- , . , , , .

#include <iostream>
using namespace std;

struct B{
    const char mem_var[];
};

struct A {
    const char * value_in_struct ;  // this line gives me a error message.
    A(char *s):value_in_struct(s){}
    A() { value_in_struct = NULL;}
};

void t(void) {
    const char value[] = "att";  // this line was ok at compiling
    std::cout << "value = " << value << std::endl;
    //value[2] = 's';  // gives error
}

int main(){
    A a(const_cast< char *>("abc"));
    A b ;
    b.value_in_struct = "bbc";
    cout <<"a: "<<a.value_in_struct << endl;
    cout <<"b: "<<b.value_in_struct << endl;
    t();
    //B bb; gives error for not initizaling mem_var
    return 0;
}

Answer 3

It has been a while since I used C ++, but can I try:

const char[] value_in_strict = {'a'};

Answer 4

struct A {
    const char value_in_struct[] = "a";.
};

It is not right. Is this a class member of a class or a member of an object? If it is a member of a class, you should write like this:

static constexpr char value_in_struct[] = "a";

Static because it is a member of the class. Constexpr because you initialize it in the class definition.

If it is a member object, you cannot initialize it in the class definition.