Thread: Not sure what I'm doing here....structures and chars a bad mix?

Any ideas here? I've spent the past hour trying to fix this, but can't quite get it to work. (very new to C)

Code:

#include <stdio.h>
#include <string.h>
#include "player.h"


int board[3][3];
int maxInput = 3; /* this represents the maximum int they can specify when choosing a position */


struct players player[2];
int isEven();


int main()
{
    player[0].name = "john";
    printf("%s", player[0].name); //hmmm
    getchar();
}

players.h

Code:

#ifndef PLAYER_H_INCLUDED
#define PLAYER_H_INCLUDED


struct players {
    char name[256];
    char type;
};


#endif // PLAYER_H_INCLUDED

Returns the error:

Code:

C:\Users\Justin\Desktop\Project\Tutorials\main.c|13|error: incompatible types when assigning to type 'char[256]' from type 'char *'|

You've just discovered why the string functions exist.
C string handling - Wikipedia, the free encyclopedia

I would use something like

Code:

player[0].name[0] = '\0';
strncat(player[0].name, "john", 254);

but it's up to you.

If i were you i would have as member of the struct char *name;
Then when i do this the pointer name would be set to the string "john"(without the double quotes).
player[0].name = "john";

Notice also the following example

Code:

char player1[] = "Kahn";
char *player2 = "Samaras";

player2 = "Papadopoulos"; /* ok */
player1 = "Karagounis"; /*error!*/

what happens here is that the char pointer can be handled as a pointer(of course :P ) ,which means that we can set it to another string.
You can not say to the array to go point in another string that Kahn.
On the other hand,
with the array you can modify the contents of the strings ,where with the char pointer you can not modify the contents of the string hope this helps

Originally Posted by whiteflags

You've just discovered why the string functions exist.
C string handling - Wikipedia, the free encyclopedia

I would use something like

Code:

player[0].name[0] = '\0';
strncat(player[0].name, "john", 254);

but it's up to you.

That's even greater!This library has some powerful functions like strcmp,strcpy,strlen etc...

If you use this you could do (with member of struct the char name[256])

Code:

strcpy(player[0].name , "john");

Thanks for the quick & helpful response! I tested the code and it worked perfectly.

Just to make sure I understand what you did there, you:

Set name to an empty string.
You then concatenated john and \0, forming: john\0 - which just outputs john

I just want to make sure I know what's going on instead of just agreeing and moving on. ^.^

Originally Posted by std10093

If i were you i would have as member of the struct char *name;
Then when i do this the pointer name would be set to the string "john"(without the double quotes).
player[0].name = "john";

Notice also the following example

Code:

char player1[] = "Kahn";
char *player2 = "Samaras";

player2 = "Papadopoulos"; /* ok */
player1 = "Karagounis"; /*error!*/

what happens here is that the char pointer can be handled as a pointer(of course :P ) ,which means that we can set it to another string.
You can not say to the array to go point in another string that Kahn.
On the other hand,
with the array you can modify the contents of the strings ,where with the char pointer you can not modify the contents of the string hope this helps

So you recommend

Code:

char *string;

vs

Code:

char mystring[length];

Correct?

Originally Posted by Justin H

Thanks for the quick & helpful response! I tested the code and it worked perfectly.

Just to make sure I understand what you did there, you:

Set name to an empty string.
You then concatenated john and \0, forming: john\0 - which just outputs john

I just want to make sure I know what's going on instead of just agreeing and moving on. ^.^

Correct.But i would also suggest you to take a loop at strcpy function as well

Originally Posted by std10093

Correct.But i would also suggest you to take a loop at strcpy function as well

Yeah, I wasn't aware of all the string functions C had available. I'll definitely be looking into them.

Originally Posted by Justin H

Yeah, I wasn't aware of all the string functions C had available. I'll definitely be looking into them.

A general tip.Don't edit the posts without letting the others know especially when posts are created one after other

Because you are new i suggest you stick with the your approach(static array) . When you feel ok with them then go for the other

And I was thinking more along the lines of when you do want to be able to use the pointer to modify the string, in which case, a pointer to a string literal can't do what you want at all. You have to get dynamic memory, and properly copy it, and manage the variable's lifetime. (Know when to and be able to call free()) It gets even more complicated if the string's memory block needs to be resized. So you really can be careless with some C tips.

Allocating a static array (like you have done) then using string functions to manipulate it is a sensible route. I'd guess that it'd cause you the least amount of problems!

You can also do:

Code:

char string[] = "hello there";
strcpy(string, "allo");  //ok


char another[];
another[] = "lalal"; // NOT allowed, have to initialise with a value

Which gives you a writable array of the size of whatever string you initialise it with. I hardly ever use this syntax -- I find it quite rare that I want to initialise and later write to a string.
For any string that you want to write to -- e.g. accept input from the user and save it there, you should allocate memory (somehow).
For strings that don't change at run time (e.g. messages for the user) you can use the char* string literal way.