Hello, lately I've been having a lot of trouble with the std::vector. Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Swi tch> Switches;
Now I have a for...loop:
int h = Switches.size() ;
for(int i=0;i<Switches. size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size( )) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i<h-1;i++){
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
7  1478 
"Hamish" <h.****@xtra.co .nz> wrote in message
news:kJ******** ***********@new s.xtra.co.nz... Hello, lately I've been having a lot of trouble with the std::vector.
Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Swi tch> Switches;
Now I have a for...loop:
int h = Switches.size() ;
for(int i=0;i<Switches. size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size( )) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i<h-1;i++){
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
std::vector<T>: :size() returns an unsigned type. Hence 0 - 1 evaluates to
something like 0xffffffff
--
Cy http://home.rochester.rr.com/cyhome/
"Cy Edmunds" <ce******@spaml ess.rochester.r r.com> wrote in message
news:YV******** **********@twis ter.nyroc.rr.co m... "Hamish" <h.****@xtra.co .nz> wrote in message
news:kJ******** ***********@new s.xtra.co.nz... Hello, lately I've been having a lot of trouble with the std::vector.
Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Swi tch> Switches;
Now I have a for...loop:
int h = Switches.size() ;
for(int i=0;i<Switches. size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size( )) equals 0, the for...loop is
still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i<h-1;i++){
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
std::vector<T>: :size() returns an unsigned type. Hence 0 - 1 evaluates to
something like 0xffffffff
or, you could use iterators:
typedef std::vector< Switch > tSwitchContaine r
typedef tSwitchContaine r::iterator tSwitchItr;
tSwitchContaine r Switches;
for ( tSwitchItr cur = Switches.begin( ); cur != Switches.end(); cur++)
{
// do stuff.....
}
nice thing about this is you could use any container and the code would
still work
-c
Hamish wrote: Hello, lately I've been having a lot of trouble with the std::vector. Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Swi tch> Switches;
Now I have a for...loop:
int h = Switches.size() ;
for(int i=0;i<Switches. size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size( )) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i<h-1;i++){
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
Switches.size() returns a vector<Switch>: :size_type which is an unsigned
integer type.
Thus vector<Switch>: :size_type(-1) is the maximum value of that type.
Your code can be fixed like this:
for(int i=0; i<Switches.size (); ++i)
/*do stuff here*/
or better:
for(vector<Swit ch>::size_type i=0; i<Switches.size (); ++i)
/*do stuff here*/
--
Ioannis Vranos http://www23.brinkster.com/noicys
"Hamish" <h.****@xtra.co .nz> wrote in message
news:kJ******** ***********@new s.xtra.co.nz... Hello, lately I've been having a lot of trouble with the std::vector.
Seems to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Swi tch> Switches;
Now I have a for...loop:
int h = Switches.size() ;
for(int i=0;i<Switches. size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size( )) equals 0, the for...loop is still
entered, and runs infinitely.
for(std::vector <Switch>::size_ type i = 0; i < Switches.size() ; ++i)
/* etc */
If for some reason you really want to ignore the last
element (if one exists):
if(!Switches.em pty())
for(std::vector <Switch>::size_ type i = 0; i < Switches.size() - 1; ++i)
/* etc */
However, if I use the line:
for(int i=0;i<h-1;i++){
then there is not a problem.
If 'h' starts at zero, the behavior is undefined.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
Vector indices begin with zero and run through 'size()' - 1
-Mike
Hamish wrote: Hello, lately I've been having a lot of trouble with the std::vector. Seems
to create unpredictable behaviour within my code.
Example:
struct Switch{
int i;
int j;
double d;
};
std::vector<Swi tch> Switches;
Now I have a for...loop:
int h = Switches.size() ;
for(int i=0;i<Switches. size()-1;i++){
/*do stuff here*/
}
The problem is, when h (Switches.size( )) equals 0, the for...loop is still
entered, and runs infinitely.
However, if I use the line:
for(int i=0;i<h-1;i++){
then there is not a problem.
Anyone got any ideas as to what is going on, cos this is ruining my New
Year!
Switches.size() returns a vector<Switch>: :size_type which is an unsigned
integer type.
Thus vector<Switch>: :size_type(-1) is the maximum value of that type.
Your code can be fixed like this:
for(int i=0; i<Switches.size (); ++i)
/*do stuff here*/
or better:
for(vector<Swit ch>::size_type i=0; i<Switches.size (); ++i)
/*do stuff here*/
--
Ioannis Vranos http://www23.brinkster.com/noicys
In article <Su************ ******@newsread 1.news.pas.eart hlink.net>,
Mike Wahler <mk******@mkwah ler.net> wrote: If for some reason you really want to ignore the last
element (if one exists):
if(!Switches.e mpty())
for(std::vecto r<Switch>::size _type i = 0; i < Switches.size() - 1; ++i)
/* etc */
Which of course is a big problem if the size is 0. When dealing with
unsigned types, I find avoiding subtraction to be much safer.
for(int i = 0; i+1 < Switches.size() ; ++i)
--
Mark Ping em****@soda.CSU A.Berkeley.EDU
"E. Mark Ping" <em****@soda.cs ua.berkeley.edu > wrote in message
news:d2******** **@agate.berkel ey.edu In article <Su************ ******@newsread 1.news.pas.eart hlink.net>,
Mike Wahler <mk******@mkwah ler.net> wrote: If for some reason you really want to ignore the last
element (if one exists):
if(!Switches.em pty())
for(std::vector <Switch>::size_ type i = 0; i < Switches.size() - 1;
++i) /* etc */
Which of course is a big problem if the size is 0.
You seem not to have noticed the test:
if(!Switches.em pty())
--
John Carson This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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