Copying struct problems [closed] - c

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Closed 10 years ago.
Assume: struct foo_t { int X,Y,Z; }. Some function take an array of struct foo_t and set some values to it; something like this:
void foo(struct foo_t *f, size_t limit, size_t *result_length)
{
int i = 0;
struct foo_t a;
a.X = 5;
//...
struct foo_t b;
b.X = 10;
// ...
struct foo_t c;
c.X = 4;
//...
f[i++] = a;
f[i++] = b;
f[i++] = c;
*result_length = i;
}
and then:
struct foo_t buf[12];
struct foo_t positive[12];
struct foo_t negative[12];
size_t len;
foo(buf, sizeof(buf)/sizeof(buf[0]), &len);
int c,positive_len,negative_len;
for(c = positive_len = negative_len = 0; c < len; c++)
{
if(buf[c].X < 8)
positive[positive_len++] = buf[c];
else
negative[negative_len++] = buf[c];
}
And finally:
puts("POSITIVE:");
int i;
for(i = 0; i < positive_len; i++)
printf("%d\n", positive[i].X);
puts("NEGATIVE:");
for(i = 0; i < negative_len; i++)
printf("%d\n", nagative[i].X);
The problem is the following: instead of getting "POSITIVE:\n4\n5", "NEGATIVE:10" I'm getting 5 and 5 and 10 isn't printed. In other words, only the last value set. Why is this happening? I've reduced significantly my code to try to get some help here because the real function is around 300 lines of code that includes database management, etc; If really needed I will post here. Before to use = operator, I'd used memcpy() to do copy of struct to my positive/negative arrays.

Answer 1

You have a typo in your code:
struct foo_t c;
b.X = 4; // this should be c.X = 4;
//...

Answer 2

You have two typos/bugs in the example above:
You are not setting c
struct foo_t c;
b.X = 4;
The variable in this printf is misspelled
for(i = 0; i < negative_len; i++)
printf("%d\n", nagative[i].X);

Answer 3

There were a couple errors. Some were spelling and "c" is never assigned to in your "foo" function.
#include <stdlib.h>
#include <stdio.h>
#include <memory.h>
typedef struct foo_t
{
int X, Y, Z;
}foo_t;
void foo(struct foo_t *f, size_t limit, size_t *result_length)
{
int i = 0;
struct foo_t a, b, c;
a.X = 5;
//...
b.X = 10;
// ...
c.X = 4; // CHANGE HERE FROM "B" to "C".
//...
f[i++] = a;
f[i++] = b;
f[i++] = c;
*result_length = i;
}
int main(int argc, char** argv)
{
// CORRECTED ALL SPELLING ERRORS!!! (POSITIVE / NEGATIVE)
struct foo_t buf[12];
struct foo_t positive[12];
struct foo_t negative[12];
size_t len;
int c, positive_len, negative_len;
foo(buf, sizeof(buf)/sizeof(buf[0]), &len);
for(c = positive_len = negative_len = 0; c < len; c++)
{
if(buf[c].X < 8)
positive[positive_len++] = buf[c];
else
negative[negative_len++] = buf[c];
}
{ // <-- IGNORE THIS BADNESS
int i;
puts("POSITIVE:");
for(i = 0; i < positive_len; i++)
printf("%d\n", positive[i].X);
puts("NEGATIVE:");
for(i = 0; i < negative_len; i++)
printf("%d\n", negative[i].X);
}
getchar();
}

Answer 4

This is an SSCCE (Short, Self-Contained, Complete Example) generated from your code:
#include <stdio.h>
struct foo_t { int X; };
static void foo(struct foo_t *f, size_t limit, size_t *result_length)
{
size_t i = 0;
struct foo_t a;
a.X = 5;
struct foo_t b;
b.X = 10;
struct foo_t c;
c.X = 4;
if (i < limit)
f[i++] = a;
if (i < limit)
f[i++] = b;
if (i < limit)
f[i++] = c;
*result_length = i;
}
int main(void)
{
struct foo_t buf[12];
struct foo_t positive[12];
struct foo_t negative[12];
size_t len;
foo(buf, sizeof(buf)/sizeof(buf[0]), &len);
size_t c,positive_len,negative_len;
for (c = positive_len = negative_len = 0; c < len; c++)
{
if (buf[c].X < 8)
positive[positive_len++] = buf[c];
else
negative[negative_len++] = buf[c];
}
puts("POSITIVE:");
for (size_t i = 0; i < positive_len; i++)
printf("%d\n", positive[i].X);
puts("NEGATIVE:");
for (size_t i = 0; i < negative_len; i++)
printf("%d\n", negative[i].X);
}
It produces:
POSITIVE:
5
4
NEGATIVE:
10
I had to fix nagative to negative and postive to positive. I initialized c.X. I used limit to ensure no overflow (and fix the warning). I changed the various int counter variables to size_t to avoid warnings about signed vs unsigned comparisons. I eliminated the Y and Z members from the structure since they aren't used in this minimal example.