Thread: struct data input problem..

in this example
we do create the same variable twice
but here on the second time we are creating robots[3] using ROBOT (which is the same type as robot type)

why is it possible??

we are creating the same variable twice

Code:

#include <stdio.h>

typedef struct robot ROBOT;

struct robot { 
  char *name; 
  int energy; 
};

int main() {
  int i;
  
  ROBOT robots[3];                              //1st time

  robots[0].name = "Lunar Lee";
  robots[0].energy = 50;
  robots[1].name = "Planetary Pete";
  robots[1].energy = 20;
  robots[2].name = "Martian Matt";
  robots[2].energy = 30;

  
  ROBOT robots[3] = { {"Lunar Lee", 50},{"Planetary Pete", 20},{"Martian Matt", 30} }; //2nd time

It is not possible.
And for goodness sake, change that struct of yours!

Code:

struct robot { 
  const char* name; 
  int energy; 
};

Error 1 error C2086: 'ROBOT robots[3]' : redefinition g:\w00t\visual studio 2008\projects\temp\temp3.cpp 13

They do not redefine the variable. It is enclosed in comments.
And despite comments, the code inside the comments actually compiled file (remember to remove the first defining of the variable).
But the example does have one thing wrong, however.
If you're going to assign string literals to variables, then use const char*, not char*.

Oh and I found this:

Instinctively, I first declared my array of robots, then I tried initializing each element one by one like this:
robots[0] = {"Lunar Lee", 50};
Unfortunately, MSVC++ complained, and so I initialized each name and energy field separately for each robot, as shown above.

I just want to point out that this is wrong, WRONG, WRONG!
MSVC is right to complain here, because it is not possible according to the standard.
Better find yourself a better tutorial... Try this site's tutorials, instead.

thanks

so curly braces can go ones only at the initialization of the variable

why do i need to change the char pointer into constant?

Originally Posted by transgalactic2

so curly braces can go ones only at the initialization of the variable

Only at the definition or declaration of a variable, as pointed out.

why do you want to change the char pointer into constant?

I already mentioned that. Try following links.
http://cpwiki.sourceforge.net/Common...kes_and_errors

if i get it correctly
string literal is a char pointer to which we initialized it using curly braces

string literals are on read only memory

and there are no way to change them after initialization

No, a string literals is something like this:
"Hello World!"
String literals are read-only, yes.
They cannot ever be changed, since they are written correctly from the start (know what I mean?).
A string literals is typically stored in a read-only place and the compiler then assigns a const char* pointer to wherever you assign or initialize it.

When initializing an array with a string literal, the string literal is copied into the buffer, so you don't need to make it constant.

Code:

char* str = "Hellq World!";
str[4] = 'o'; // Oops. Error at runtime.
char str2[] = "Hellq World!";
str2[4] = 'o'; // OK
const char* str3 = "Hellq World!";
str3[4] = 'o'; // Oops. Compile error.

When assigning to (or initializing) pointers, yes, then the pointer should be const (pointer to const char).