Struct class iteration ...

[Mario]

Hy, I have the fallowing code and I don't understand why is not
working ...

in a header file:

typedef void* cheie;
typedef void* valoare;

struct _Tabel;
typedef _Tabel* Tabel;

struct _Tabel{
cheie valuta[10];
valoare lei[10];
int dim;
};
in a cpp file I have the creating function, and a function for
inserting components. It is all working very fine, except when I want
to type the content of the Tabel struct ...
If I write smt like this:
int i=t->dim; //where t->dim is the number of components
while (i>0)
{
cout<<(char*)t->valuta[i];
i--;
}
the program crash ...
if I do smt like this:
int i=t->dim; //where t->dim is the number of components
int p=0;
t->dim=0;
while (t->dim<i)
{
cout<<(char*)t->valuta[t->dim];
t->dim++;
}
t->dim=i;
it prints only the last value in the vector for t->dim times. Although
very complicated and not elegant, this is the only way I got it to
print smt ...
I don't understand why in the first case the program just crashes and
in the second one is not working properly ... And I can't to things in
other maners because is a school project. If someone can explain me
where I am going wrong, I will be very grateful!
Thanks!

[Thomas Tutone]

Mario wrote:

Hy, I have the fallowing code and I don't understand why is not
working ...

in a header file:

typedef void* cheie;
typedef void* valoare;

struct _Tabel;

An underscore followed by a capital letter (as you do above) means
Undefined Behavior.

typedef _Tabel* Tabel;

struct _Tabel{
cheie valuta[10];
valoare lei[10];
int dim;
};
in a cpp file I have the creating function, and a function for
inserting components. It is all working very fine, except when I want
to type the content of the Tabel struct ...
If I write smt like this:
int i=t->dim; //where t->dim is the number of components
while (i>0)
{
cout<<(char*)t->valuta[i];

C-style casts (like you do above) and casting to and from void* is
generally a bad idea, because it often masks underlying problems.

i--;
}
the program crash ...
if I do smt like this:
int i=t->dim; //where t->dim is the number of components
int p=0;
t->dim=0;
while (t->dim<i)
{
cout<<(char*)t->valuta[t->dim];
t->dim++;
}
t->dim=i;
it prints only the last value in the vector for t->dim times. Although
very complicated and not elegant, this is the only way I got it to
print smt ...
I don't understand why in the first case the program just crashes and
in the second one is not working properly ... And I can't to things in
other maners because is a school project. If someone can explain me
where I am going wrong, I will be very grateful!

This is answered in the FAQ:

http://www.parashift.com/c++-faq-lit...t.html#faq-5.8

Good luck.

Best regards,

Tom

[Howard Gardner]

typedef void* cheie;

make this:

typedef char * cheie;

cout<<(char*)t->valuta[i];

and make this:

cout << t->valuta[i];

There is code that you haven't shown us. Somewhere you are writing lines
like:

t->valuta[i] = SOMETHING;

If something is not a char *, then the code you wrote isn't going to
work. Changing the typedef of cheie to char * will make the mistake obvious.

[Mario]

Howard Gardner wrote:

typedef void* cheie;

make this:

typedef char * cheie;

cout<<(char*)t->valuta[i];

and make this:

cout << t->valuta[i];

There is code that you haven't shown us. Somewhere you are writing lines
like:

t->valuta[i] = SOMETHING;

If something is not a char *, then the code you wrote isn't going to
work. Changing the typedef of cheie to char * will make the mistake obvious.

No, I do all the necessary casts, remember I sad that the creating and
the inserting functions ar going allright. The only problem is that I
can't figure why you can't just write
t->valuta[i] ???
if i write the value of t->dim, before I write lets say t->dim=123, it
does prints 123, but the printed value of t->valuta[t->dim] is the
last value inserted ... and a didn't find the logic in all this ... So
.... I hope for other ideas ...

[Pete Becker]

Mario wrote:

Hy, I have the fallowing code and I don't understand why is not
working ...

in a header file:

typedef void* cheie;
typedef void* valoare;

struct _Tabel;
typedef _Tabel* Tabel;

struct _Tabel{
cheie valuta[10];
valoare lei[10];
int dim;
};
in a cpp file I have the creating function, and a function for
inserting components. It is all working very fine, except when I want
to type the content of the Tabel struct ...
If I write smt like this:
int i=t->dim; //where t->dim is the number of components
while (i>0)
{
cout<<(char*)t->valuta[i];
i--;
}

When t->dim is the number of components, they would ordinarily be
located in valuta[0] through valuta[t->dim - 1]. Move the i-- up above
the cout statement to get the indexing right. If you've used similar
code to set the values, chances are that somewhere the code set the
value of valuta[10], which isn't valid. Array indexes run from 0 to one
less than the size of the array.

the program crash ...
if I do smt like this:
int i=t->dim; //where t->dim is the number of components
int p=0;
t->dim=0;
while (t->dim<i)
{
cout<<(char*)t->valuta[t->dim];
t->dim++;
}
t->dim=i;
it prints only the last value in the vector for t->dim times. Although
very complicated and not elegant, this is the only way I got it to
print smt ...
I don't understand why in the first case the program just crashes and
in the second one is not working properly ... And I can't to things in
other maners because is a school project. If someone can explain me
where I am going wrong, I will be very grateful!
Thanks!

int i = 0;
while (i < t->dim)
{
cout << (char*)t->valuta[i] << '\n';
++i;
}

That does the same thing as the preceding code snippet, but much more
clearly. It doesn't explain why your code prints only the last value,
multiple times. But I suspect that the actual code was different from
this code.