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Home > Forums > Programmers > Languages > C++: Microsoft Forum

ANSI C structures, how to pass a value to

CODE

#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 (Programmer)

11 Nov 10 11:04

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 (MIS)

11 Nov 10 11:29

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

CODE

// 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 (Programmer)

11 Nov 10 11:37

same as in the other post:

CODE

char* thename = {0};

try defining the struct outside/above the definition of main

SDowd (Programmer)

11 Nov 10 11:42

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

CODE

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 (MIS)

11 Nov 10 11:49

Program now crashes here is latest code

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)

CODE

#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 (Programmer)

11 Nov 10 11:55

after these lines:

CODE

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

add

CODE

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

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

DougP (MIS)

11 Nov 10 11:56

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 (Programmer)

11 Nov 10 12:12

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:

CODE

sample Asample; //instance of defaulted struct

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

//verify "thename" contains what you expect
printf("thename = %s\n", thename);

Then do the set to the struct:

CODE

Asample.name = thename;

DougP (MIS)

11 Nov 10 12:46

Thanks.

DougP

SDowd (Programmer)

11 Nov 10 14:21

Did any of that help fix it?

DougP (MIS)

11 Nov 10 14:29

nope

DougP

SDowd (Programmer)

11 Nov 10 15:42

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

CODE

// 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:

CODE

Enter name
bob
the name = bob
bob

SDowd (Programmer)

11 Nov 10 16:25

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

cpjust (Programmer)

12 Nov 10 15:40

Quote (SDowd):
char* thename = {0};

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

Either use an array:

CODE

char thename[80];

or allocate some memory for the pointer:

CODE

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

SDowd (Programmer)

12 Nov 10 17:33

it is an array

cpjust (Programmer)

13 Nov 10 22:41

What's an array?

char* is a pointer.

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