struct point not identified by gcc

[DanielJohnson]

I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors. The
main ones are : useless storage class specifier in empty declaration,
'point' undeclared (first use in this function), 'p1' undeclared
(first use in this function) etc. Any help will be appreciated. Thanks

#include <stdio.h>
#include <math.h>

/* create a 3d point struct*/
typedef struct point{
int x,y,z;
};

/* Function declaration*/
float dist(point *, point *);
point add(point *, point *);
void display(point *);

int main(void)
{
point p1,p2,p3;
p1.x=2;p1.y=4;p 1.z=5;
p2.x=5;p1.y=2;p 1.z=6;
printf("\n dist = %f", dist(&p1,&p2));
add(&p1, &p2);
display(&p3);
return;
}

float dist(point *a, point *b)
{
float length=0.0;
length = sqrt( (a->x-b->x)*(a->x-b->x)+ (a->y-b->y)*(a->y-b->y)+
(a->z-b->z)*(a->z-b->z));
return length;
}

point add(point *a, point *b)
{
point temp;
temp.x=a->x + b->x;
temp.y=a->y + b->y;
temp.z=a->z + b->z;
return temp;
}

void display(point *a)
{
printf("\npoint = %d,%d,%d\n",a->x,a->y,a->z);
}

[user923005]

On Feb 22, 9:27 am, "DanielJohn son" <diffuse...@gma il.comwrote:

I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors. The
main ones are : useless storage class specifier in empty declaration,
'point' undeclared (first use in this function), 'p1' undeclared
(first use in this function) etc. Any help will be appreciated. Thanks

#include <stdio.h>
#include <math.h>

/* create a 3d point struct*/
typedef struct point{
int x,y,z;

};

/* Function declaration*/
float dist(point *, point *);
point add(point *, point *);
void display(point *);

Try:
typedef struct tag_point {
int x,y,z;
} point;

>From the C FAQ:

Section 2. Structures, Unions, and Enumerations

2.1: What's the difference between these two declarations?

struct x1 { ... };
typedef struct { ... } x2;

A: The first form declares a "structure tag"; the second declares a
"typedef". The main difference is that you subsequently refer
to the first type as "struct x1" and the second simply as "x2".
That is, the second declaration is of a slightly more abstract
type -- its users don't necessarily know that it is a structure,
and the keyword struct is not used when declaring instances of it.

2.2: Why doesn't

struct x { ... };
x thestruct;

work?

A: C is not C++. Typedef names are not automatically generated for
structure tags. See also question 2.1 above.

[snip]

[santosh]

DanielJohnson wrote:

I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors. The
main ones are : useless storage class specifier in empty declaration,
'point' undeclared (first use in this function), 'p1' undeclared
(first use in this function) etc. Any help will be appreciated. Thanks

#include <stdio.h>
#include <math.h>

/* create a 3d point struct*/
typedef struct point{
int x,y,z;
};

Change this to:

typedef struct {
int x;
int y;
int z;
} point;

/* Function declaration*/
float dist(point *, point *);
point add(point *, point *);
void display(point *);

int main(void)
{
point p1,p2,p3;
p1.x=2;p1.y=4;p 1.z=5;
p2.x=5;p1.y=2;p 1.z=6;

Why not use more whitespace to aid in clarity? You also seem to be
overwriting the values in p1.y and p1.z.

printf("\n dist = %f", dist(&p1,&p2));

Add a newline after %f as well. Also as per the initialisations given
above, p2.y, p2.z, p3.x, p3.y, p3.z are all uninitialised. If you
operate on uninitialised objects you'll most likely get back useless
results.

add(&p1, &p2);

The function add returns a local object, (as given below). You're not
assigning the return value to anything here, thus loosing it.

display(&p3);
return;

Return an explicit value; don't return random values.

}

float dist(point *a, point *b)
{
float length=0.0;
length = sqrt( (a->x-b->x)*(a->x-b->x)+ (a->y-b->y)*(a->y-b->y)+
(a->z-b->z)*(a->z-b->z));

You do realise that b->y and b->z are uninitialised don't you? You
might also want to split up the messy function call into more readable
steps.

return length;
}

point add(point *a, point *b)
{
point temp;
temp.x=a->x + b->x;
temp.y=a->y + b->y;
temp.z=a->z + b->z;
return temp;
}

void display(point *a)
{
printf("\npoint = %d,%d,%d\n",a->x,a->y,a->z);
}

Correct these errors and try to compile again.

[DanielJohnson]

On Feb 22, 12:43 pm, "santosh" <santosh....@gm ail.comwrote:

DanielJohnson wrote:

I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors. The
main ones are : useless storage class specifier in empty declaration,
'point' undeclared (first use in this function), 'p1' undeclared
(first use in this function) etc. Any help will be appreciated. Thanks

#include <stdio.h>
#include <math.h>

/* create a 3d point struct*/
typedef struct point{
int x,y,z;
};

Change this to:

typedef struct {
int x;
int y;
int z;
} point;

/* Function declaration*/
float dist(point *, point *);
point add(point *, point *);
void display(point *);

int main(void)
{
point p1,p2,p3;
p1.x=2;p1.y=4;p 1.z=5;
p2.x=5;p1.y=2;p 1.z=6;

Why not use more whitespace to aid in clarity? You also seem to be
overwriting the values in p1.y and p1.z.

printf("\n dist = %f", dist(&p1,&p2));

Add a newline after %f as well. Also as per the initialisations given
above, p2.y, p2.z, p3.x, p3.y, p3.z are all uninitialised. If you
operate on uninitialised objects you'll most likely get back useless
results.

add(&p1, &p2);

The function add returns a local object, (as given below). You're not
assigning the return value to anything here, thus loosing it.

display(&p3);
return;

Return an explicit value; don't return random values.

}

float dist(point *a, point *b)
{
float length=0.0;
length = sqrt( (a->x-b->x)*(a->x-b->x)+ (a->y-b->y)*(a->y-b->y)+
(a->z-b->z)*(a->z-b->z));

You do realise that b->y and b->z are uninitialised don't you? You
might also want to split up the messy function call into more readable
steps.

return length;
}

point add(point *a, point *b)
{
point temp;
temp.x=a->x + b->x;
temp.y=a->y + b->y;
temp.z=a->z + b->z;
return temp;
}

void display(point *a)
{
printf("\npoint = %d,%d,%d\n",a->x,a->y,a->z);
}

Correct these errors and try to compile again.

I did all your changes and now I get this error

undefined reference to `sqrt'

Is math.sqrt() correct or just sqrt()

[u plz]

On Thu, 22 Feb 2007 09:27:06 -0800, DanielJohnson wrote:

I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors. The
main ones are : useless storage class specifier in empty declaration,
'point' undeclared (first use in this function), 'p1' undeclared
(first use in this function) etc. Any help will be appreciated. Thanks

#include <stdio.h>
#include <math.h>

/* create a 3d point struct*/
typedef struct point{
int x,y,z;
};

You need a name for the typedef, so you could do something like:

typedef struct {
int x, y, z;
} point;

-Alok

[santosh]

DanielJohnson wrote:

On Feb 22, 12:43 pm, "santosh" <santosh....@gm ail.comwrote:

DanielJohnson wrote:

I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors.

<snip code and corrections>

Correct these errors and try to compile again.

I did all your changes and now I get this error

undefined reference to `sqrt'

Under most UNIX systems, the math library is seperate and not linked
in by default. Add the '-lm' command line switch, (without the
quotes), to cc when you compile it.

Is math.sqrt() correct or just sqrt()

The latter, with an argument. The former is C++.

[santosh]

santosh wrote:

DanielJohnson wrote:

On Feb 22, 12:43 pm, "santosh" <santosh....@gm ail.comwrote:

DanielJohnson wrote:
I wrote a simply program with a 3 D coordinate called point. I am
adding two points, taking their distance etc. gcc compiler is not
identifying the struct. Here is the code. I get bunch of errors.

<snip code and corrections>

Is math.sqrt() correct or just sqrt()

The latter, with an argument. The former is C++.

Correction: It's not even C++.

[DanielJohnson]

Here is the updated program but it doesnt compile and says undefined
refrence to sqrt. Can you please tell whats going wrong in this
variant of the program.
#include <stdio.h>
#include <math.h>

/* create a 3d point struct*/
typedef struct{
int x;
int y;
int z;
} point;

/* Function declaration*/
double dist(point *, point *);
point add(point *, point *);
void display(point *);

int main(void)
{
point p1,p2,p3;
p1.x=2;p1.y=4;p 1.z=5;
p2.x=5;p2.y=2;p 2.z=6;
printf("\n dist = %lf \n", dist(&p1,&p2));
p3 = add(&p1, &p2);
display(&p3);
return 0;
}

double dist(point *a, point *b)
{
double length=0.0;
length = sqrt( (a->x-b->x)*(a->x-b->x) + (a->y-b->y)*(a->y-b->y)+
(a->z-b->z)*(a->z-b->z) );
return length;
}

point add(point *a, point *b)
{
point temp;
temp.x=a->x + b->x;
temp.y=a->y + b->y;
temp.z=a->z + b->z;
return temp;
}

void display(point *a)
{
printf("\npoint = %d,%d,%d\n",a->x,a->y,a->z);
}

[DanielJohnson]

Under most UNIX systems, the math library is seperate and not linked

in by default. Add the '-lm' command line switch, (without the
quotes), to cc when you compile it.

Is math.sqrt() correct or just sqrt()

The latter, with an argument. The former is C++.

Thanks it worked. Do I always need to compile using -lm switch. I was
completely unawre if this.

[user923005]

On Feb 22, 10:20 am, "DanielJohn son" <diffuse...@gma il.comwrote:

Under most UNIX systems, the math library is seperate and not linked
in by default. Add the '-lm' command line switch, (without the
quotes), to cc when you compile it.

Is math.sqrt() correct or just sqrt()

The latter, with an argument. The former is C++.

Thanks it worked. Do I always need to compile using -lm switch. I was
completely unawre if this.

How did you miss this when you read the C-FAQ:

14.3: I'm trying to do some simple trig, and I am #including <math.h>,
but I keep getting "undefined: sin" compilation errors.

A: Make sure you're actually linking with the math library. For
instance, under Unix, you usually need to use the -lm option, at
the *end* of the command line, when compiling/linking. See also
questions 13.25, 13.26, and 14.2.