Add data to array inside struct

Question

How can I set data into the array of 3 rows which at the same time has an array of 4 elements?

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

typedef struct
{
    char value[6];
} MyType;

typedef struct
{
    int size;
    MyType *values;
} NewType;

static NewType car;
static MyType mytype = {{'\0'}};

void Init(NewType *car)
{
    car->size = 3; // Will contain 3 rows of 4 elements
    car->values = (MyType*) calloc(car->size,sizeof(MyType));
}

// Get data into
void Write(NewType *car, MyType *data)
{
   strcpy(car->values[0].value, data[0].value); // ** Here is where complains

   printf("%d\n", car->values[0]); // Printing wrong data!
}

int main()
{
    Init(&car);

    strcpy(mytype.value, "Hello"); 

    Write(&car, &mytype);

    system("PAUSE");
}

What do you expect the printf to show? If you change it to printf("%s\n", car->values[0].value);, then it will print Hello. — juan.facorro
– juan.facorro, Commented Mar 9, 2014 at 2:53

juan.facorro · Accepted Answer · 2014-03-09 03:01:20Z

1

In this piece of code strcpy(mytype.value, "Hello"); you are copying a 5 letters string into an array of 4 chars, which is illegal, so that might be causing the error. Either change the string you copy to mytype.value for a shorter one (like "Bye") or increase the number of elements in the value char array to the number of characters of the word you want to put in there plus one for the terminating null character.

Additionally the printf() statement in the Write() function has a format string that indicates to print an int, which I doubt is what you actually want. The following are the rewritten Write() and main() functions.

void Write(NewType *car, MyType *data)
{
   strcpy(car->values[0].value, data->value);

   printf("%s\n", car->values[0].value); 
}

int main()
{
    Init(&car);

    strcpy(mytype.value, "Bye"); 

    Write(&car, &mytype);

    system("PAUSE");
}

answered Mar 9, 2014 at 3:01

juan.facorro

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2 Comments

juan.facorro Over a year ago

@valter You are correct in that values is a pointer so the -> would also work, but the values pointer is conceived as a collection of values and both expressions are equivalent (values->value = values[0].value, (values + 1)->value = values[1].value, and so on) so it's just a matter of preference in this case.

γηράσκω δ' αεί πολλά διδασκόμε Over a year ago

Yes of course! (*values).value is the same as values->value. silly me.

Arjun Sreedharan · Accepted Answer · 2014-03-09 05:40:09Z

0

In your printf("%d\n", car->values[0]) you are actually trying to print the first 4 bytes of the memory you have calloced inside your Init(), formatted as a signed decimal integer. (4 in case of x86. sizeof(int) in general).

To print the value, you should:

printf("%s\n", car->values->value);

answered Mar 9, 2014 at 5:40

Arjun Sreedharan

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