Initialization of values in struct - C ++

The error that you present to us is due to the following:

unsigned int total=base+dietes;

You are trying to initialize the value total with base and dietes does not have a designated value, so the compiler tells you this warning, because unlike classes, default structures can not be initialized in the statement, BUT There is a solution.

Voila The solution:

struct salari{
  unsigned int base;
  unsigned int dietes;
  unsigned int total;

  salari(){
   base = 0;
   dietes = 0;
   total = base + dietes;
  }
};

This is a way to make a kind of constructor for structures in C ++, with this you can initialize each of the values contained in the structure, without you throwing any error.

After this the output is:

100
2
0

In this case, it throws 0 at the end because this is the value with which we have initialized it, you must assign it the value you want later, since the structure does not update its values every time you call it, that is, if you tell him that an element will be equal to the sum of others, that is the value of the declaration and initialization , then you must change it according to your needs.

In C ++, unlike C # and Java, it was not allowed to initialize member variables in the place of the declaration. This was until in August 2011 the C ++ 11 standard was approved, adding this functionality to the standard behavior of the language.

[Here] you have the description of this functionality on the Bjarne Stroustrup (In English), receives the technical name of Initialization of members in class (" In-class member initializers ").

The gcc compiler.

Initialization of members in class is supported in gcc from the version 4.7 1 . To use the C ++ 11 features, you must activate the C ++ 11 mode of the compiler by adding the -std=c++11 parameter to the compilation order, as indicated by the alarm you get when compiling:

warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11
unsigned int total=base+dietes;

So you should stop having that alarm if you compile in this way:

g++ base_dades.cc -o base_dades.e -std=c++11

Surely you have a gcc version equal to or higher than 4.7, so the code compiles despite being the wrong code in C ++ standards prior to C ++ 11. As the compile parameter -std=c++11 is not added by default, it shows an alarm (instead of an error) for being able to compile the code despite the absence of the appropriate compilation option.

Initialization of members in class operation

I have the feeling (correct me if I'm wrong) that you expected the output of your code to be:

100
2
102

But this would not happen as the unsigned int total=base+dietes; instruction is executed at the time of the instance construction of salari , that is: at the same time as the% instruction salari a; is executed.

Since members base and dietes have no initial value, their value is indeterminate 2 but not infrequently is a value different from 0. So the value 4196768 that you have obtained is the result of adding two random memory values at the time of construct a .

For the total to be automatically updated when assigning base and dietes you should use assignment functions:

struct salari{
unsigned int base = 0;
unsigned int dietes = 0;
unsigned int total = 0;

void assigna_base(unsigned int valor){
base = valor;
total = base + dietes;
}

void assigna_dietes(unsigned int valor){
dietes = valor;
total = base + dietes;
}
};

So, your main with these functions:

int main(){
salari a;
a.assigna_base(100);
a.assigna_dietes(2);

std::cout << a.base   << '\n'
          << a.dietes << '\n'
          << a.total  << '\n';

return 0;
}

I would give this exit

100
2
102

Notice that I have initialized 0 all members of salari with Initialization of members in class.

Molta sort Pol, fins an altra:)

1 [Here] you can see the features added to C ++ and in which version of gcc were implemented.

2 Any uninitialized data contains as a value that which contains the memory assigned to it, which could be any value.