ANSI C structures, how to pass a value to

[DougP]

here is my code if I hard code something it works fine. but that's not real world. I want to prompt for some values but I can't seem to get them to work. i.e. Enter your name and pass that to Asample.name

#include <stdafx.h>
#include <stdio.h>


int main( void )
{ 
	struct sample{
		char *name;
		char *addr;
		char *city;
		char *state;
		char *zip;
		char *phone;
	};
	struct sample Asample ;
	char thename;
	printf("Enter Name");
	scanf("%s",thename); 
	//Asample.name = "Fred";  < this works

Asample.name= thename; //  this does not
	printf("%s\n",Asample.name);

   return 0; /* indicates successful termination */
} /* end main */

DougP

 

[SDowd]

char thename will only accept a single char, you would need to make it a char array or a char*.

http://www.cplusplus.com/reference/clibrary/cstdio/scanf/

 

[DougP]

Ok so now I get these two errors
Warning 3 warning C4700: uninitialized local variable 'thename' used 21

char *thename;

Warning 4 warning C4700: uninitialized local variable 'Asample' used 30

// percentS.cpp : Defines the entry point for the console application.
//
#include <stdafx.h>
#include <stdio.h>

int main( void )
{ 
	int d;
	struct sample{
		char *name;
		char *addr;
		char *city;
		char *state;
		char *zip;
		char *phone;
	};
	struct sample Asample ;
	char *thename;       /* line 21 */
	printf("Enter Name");
	scanf("%s",thename);

Asample.name= thename;
	printf("%s\n",Asample.name);

	printf("%s\n",Asample.name);
	printf("%s\n",Asample.addr);
	printf("%s\n",Asample.city);  /* line 30 */
	printf("%s\n",Asample.state); 
	printf("%s\n",Asample.zip);
	printf("%s\n",Asample.phone);

	printf("Enter a number");
	scanf("%d",&d);

   return 0; /* indicates successful termination */
} /* end main */

DougP

 

[SDowd]

same as in the other post:

char* thename = {0};

try defining the struct outside/above the definition of main

 

[SDowd]

also, you may want to create a constructor for the struct which defaults the members:

struct sample{
        char *name;
        char *addr;
        char *city;
        char *state;
        char *zip;
        char *phone;

        //constructor with initializer list(everything to 0)
        sample() :
        name(0),
        addr(0),
        city(0),
        state(0),
        zip(0),
        phone(0)
        {}
    };

 

[DougP]

Program now crashes here is latest code

int main( void )
{ 
	int d;
	struct sample{
		char *name;
		char *addr;
		char *city;
		char *state;
		char *zip;
		char *phone;
	};
	struct sample Asample ={""} ;
	char *thename=NULL;
	printf("Enter Name");
	scanf("%s",thename);


Asample.name= thename;
	printf("%s\n",Asample.name);


	printf("Enter a number");
	scanf("%d",&d);

   return 0; /* indicates successful termination */
} /* end main */

(BTW I'm using Microsoft C++ now as my editor)
it compiles and runs I enter a name like Fred
then it crashes.
this is the code it brings up when it crashes, it stops on this line (the popup windows name is input.c)

#ifndef _UNICODE
                                    *(char *)pointer = (char)ch;  /* stops on this line */
                                    pointer = (char *)pointer + 1;

here is the description at the top of input.c
---------
*input.c - C formatted input, used by scanf, etc.
*
* Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
* defines _input() to do formatted input; called from scanf(),
* etc. functions. This module defines _cscanf() instead when
* CPRFLAG is defined. The file cscanf.c defines that symbol
* and then includes this file in order to implement _cscanf().
*
*Note:
* this file is included in safecrt.lib build directly, plese refer
* to safecrt_[w]input_s.c
-------------


DougP

 

[SDowd]

after these lines:

printf("Enter Name");
scanf("%s",thename);

add

printf("thename = %s\n", thename);

see if you can see what the actual value is prior to doing anything with the structure.

 

[DougP]

it is crashing on this line
Asample.name= thename;

so we're back to square one!!!!

how to pass a string that is not hard coded to something???

DougP

 

[SDowd]

print out "thename" as soon as you do your scanf. move the struct above the definition of "int main." Include the default constructor with the initializer list.

in main:

sample Asample; //instance of defaulted struct

...
printf("Enter Name");
scanf("%s",thename);

//verify "thename" contains what you expect
[COLOR=red]printf("thename = %s\n", thename);[/color]

Then do the set to the struct:

Asample.name = thename;

 

[DougP]

Thanks.


DougP

 

[SDowd]

Did any of that help fix it?

 

[DougP]

nope

DougP

 

[SDowd]

i changed "thename" to a char array and it worked for me:

// Test.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <stdio.h>


//struct definition
struct sample
{
	char *name;
	char *addr;
	char *city;
	char *state;
	char *zip;
	char *phone;

	//constructor with initializer list(everything to 0)
    sample() :
		name(0),
		addr(0),
		city(0),
		state(0),
		zip(0),
		phone(0)
		{
			//empty ctor body

		}
};



int _tmain(int argc, _TCHAR* argv[])
{
	//struct object
	sample Asample;

	char thename[100] = {0};
    printf("Enter Name\n");
    scanf("\t%s", thename, 4); 


	printf("thename = %s\n", thename);

	Asample.name = thename; //  this does not
    printf("%s\n", Asample.name);


	return 0;
}

with output of:

Enter name
bob
the name = bob
bob

 

[SDowd]

As a note, the extra param of "4" in the call to scanf is not necessary.

 

[cpjust]

char* thename = {0};

NOTE: This does NOT allocate any memory for the pointer. It just sets the pointer to NULL.

Either use an array:

char thename[80];

or allocate some memory for the pointer:

char* thename = malloc( 80 * sizeof(char) );

 

[SDowd]

it is an array

 

[cpjust]

What's an array?

char* is a pointer.