how to read values from a structure in C

Question

#include<stdio.h>
#define msize 4096

struct memory
{
    int a[msize];
};

void main()
{
    struct memory m;
    m.a[0]=250; // temperature value of 25,0
    m.a[4]=01; // heater status OFF
    m.a[8]=240; // temperature value of 24,0
    m.a[12]=00; // heater status ON
    m.a[16]=220; // temperature value of 22,0
    m.a[20]=00; // heater status ON
    read(&m);

}

void read(struct memory m)
{
    int i;
    for(i=0;i<sizeof(msize);i++)
    {
        scanf("%d", m.a[i]);
    }
}

My code creates a structure of size 4096 bytes, an object for the structure and then assigns values to i.

On compilation, the compiler throws a "first defined here" error in the read function.

Also, can someone please help me to convert this read value to ASCII?

When there's an error you should show it in the question - the compiler is trying to help. — sje397, May 08 '13 at 09:19
`sizeof(msize) != 4096` and `sizeof(struct memory) != 4096` and `void read(struct memory *m)` //read arg pointer — BLUEPIXY, May 08 '13 at 09:23

simonc · Answer 1 · 2013-05-08T09:25:10.870

3

You need to pass scanf an address to write to so need to change

scanf("%d", m.a[i]);

to

scanf("%d", &m.a[i]);
//          ^

You should also consider passing a pointer to m to read rather than passing this huge struct by value

void read(struct memory* m)
{
    int i;
    for(i=0;i<msize;i++)
    {
        scanf("%d", &m->a[i]);
    }
}

(In fact your read(&m) call in main appears to already by assuming this update.)

edited May 08 '13 at 09:25

answered May 08 '13 at 09:18

simonc

41,632
12
85
103

I changed as above Then also its throwing an error within void read() as multiple definition of read and first defined here. – user2306769 May 08 '13 at 09:47
1

You need to either move `read` above `main` or provide a forward declaration above `main`. See the answer from sje397 for details. – simonc May 08 '13 at 09:55

score 1 · Answer 2 · answered May 08 '13 at 09:21

1

In addition to what @simonc said, you should also declare the function up the top:

#include<stdio.h>
#define msize 4096

struct memory
{
int a[msize];
};

void read(struct memory m);

void main()
{
//...

answered May 08 '13 at 09:21

sje397

41,293
8
87
103

I made changes as you said then also its throwing an error as multiple definition of read and first defined here in void read function(). – user2306769 May 08 '13 at 10:03
If you paste the exact text of the error that would help a lot. Try changing your function name - `read` is common. – sje397 May 09 '13 at 09:53

score 0 · Answer 3 · answered May 08 '13 at 10:12

0

#include<stdio.h>
#define msize 4096
struct memory
{
int a[msize];
};

void read(struct memory *m)
{
int i;
for(i=0;i<sizeof(msize);i++)
 {
    scanf("%d",&m->a[i]);
 }
}

int main()
{
struct memory m;
m.a[0]=250; // temperature value of 25,0
m.a[4]=01; // heater status OFF
m.a[8]=240; // temperature value of 24,0
m.a[12]=00; // heater status ON
m.a[16]=220; // temperature value of 22,0
m.a[20]=00; // heater status ON
read(&m);
return 0;
}

answered May 08 '13 at 10:12

Coffee_lover

545
6
15

1

1. return type of main cant be void 2. read should have been placed before main 3.as @simonic already said use scanf("%d", &m->a[i]) it will compile fine without any error – Coffee_lover May 08 '13 at 10:14
thank you very much!!! could you give me some ideas to convert this values to ASCII ?? – user2306769 May 08 '13 at 10:33

how to read values from a structure in C

3 Answers3