C / C++ / MFC

4-Sep-08 19:47

Hello everyone,

String of STL does not contain trim/toupper/tolower, currently I always implement them manually. For trim, I use find first/last not of space technique, and for toupper/tolower, I always change them manually by adding some value to 'a' to form 'A' or vice versa.

My question is I want to find some best practices to implement them (one reason is I think my private implementation may be error prone and the other reason is I am not sure whether there is existing APIs which could be utilized) and comment about my current implementation issues.

thanks in advance,
George

Nibu babu thomas4-Sep-08 19:59

4-Sep-08 19:59

George_George wrote:
For trim, I use find first/last not of space technique, and for toupper/tolower, I always change them manually by adding some value to 'a' to form 'A' or vice versa.

My question is I want to find some best practices to implement them (one reason is I think my private implementation may be error prone and the other reason is I am not sure whether there is existing APIs which could be utilized) and comment about my current implementation issues.

For tolower and toupper use std::transform.

std::string Str = "nibu babu thomas";
std::transform( Str.begin(), Str.end(), Str.begin(), toupper );
std::cout << Str;

Nibu babu thomas
Microsoft MVP for VC++

Code must be written to be read, not by the compiler, but by another human being.

Programming Blog: http://nibuthomas.wordpress.com

George_George4-Sep-08 20:04

4-Sep-08 20:04

Thanks Nibu!

How about trim? No built-in APIs?

regards,
George

Nibu babu thomas4-Sep-08 21:03

4-Sep-08 21:03

George_George wrote:
How about trim? No built-in APIs?

I couldn't find one for std::string, but here is a simple routine using std functions you mentioned in your first post...

void Trim( const std::string& StrToTrim, std::string& TrimmedString )
{
   std::string::size_type First = StrToTrim.find_first_not_of( ' ' ); // Find first non space char
   std::string::size_type Last = StrToTrim.find_last_not_of( ' ' ) + 1; // First first last non space char
   TrimmedString = StrToTrim.substr( First, Last - First ); // Return substring
}

int main()
{
   std::string StrToTrim = "   32  Nibu babu thomas   2342 2 23 3    ";
   std::string TrimmedString = "On return will hold trimmed string";
   Trim( StrToTrim, TrimmedString );
   
   return 0;
}

There might be other options that could perform better than this but this one is neat!

Nibu babu thomas
Microsoft MVP for VC++

Code must be written to be read, not by the compiler, but by another human being.

Programming Blog: http://nibuthomas.wordpress.com

George_George4-Sep-08 21:40

4-Sep-08 21:40

Cool Nibu!

I want to find all possible exception which may be thrown from STL functions, for example, string.substr may throw out of range exception. But such information can not be found from MSDN. Do you have any reference documents?

regards,
George

Nibu babu thomas4-Sep-08 21:48

4-Sep-08 21:48

George_George wrote:
Do you have any reference documents?

Most of them are in the files exception and stdexcept. Note that there is no .h in these file names.

Nibu babu thomas
Microsoft MVP for VC++

Code must be written to be read, not by the compiler, but by another human being.

Programming Blog: http://nibuthomas.wordpress.com

George_George4-Sep-08 21:58

4-Sep-08 21:58

Thanks Nibu,

1.

No document which describes all possible exceptions may be thrown by a specific STL function, like string.substr?

2.

"the files exception and stdexcept" -- yes, but for a specific STL function like string.substr, how do you check all possible exceptions may be thrown by looking at the file? Smile | :)

regards,
George

Nibu babu thomas4-Sep-08 22:19

4-Sep-08 22:19

George_George wrote:
1.

No document which describes all possible exceptions may be thrown by a specific STL function, like string.substr?

2.

"the files exception and stdexcept" -- yes, but for a specific STL function like string.substr, how do you check all possible exceptions may be thrown by looking at the file? Smile

I am not sure where you can find them, but here is a more secure version of Trim.

void Trim( const std::string& StrToTrim, std::string& TrimmedString )
{
   // Find first non whitespace char in StrToTrim
   std::string::size_type First = StrToTrim.find_first_not_of( ' ' );
   // Check whether something went wrong?
   if( First == std::string::npos )
   {
      First = 0;
   }

   // Find last non whitespace char from StrToTrim
   std::string::size_type Last = StrToTrim.find_last_not_of( ' ' );
   // If something didn't go wrong, Last will be recomputed to get real length of substring
   if( Last != std::string::npos )
   {
      Last = ( Last + 1 ) - First;
   }

   // Copy such a string to TrimmedString
   TrimmedString = StrToTrim.substr( First, Last );
}

Earlier function will throw an out_of_range exception if we gave a string like " " for trimming. This one doesn't. Wink | ;)

Nibu babu thomas
Microsoft MVP for VC++

Code must be written to be read, not by the compiler, but by another human being.

Programming Blog: http://nibuthomas.wordpress.com

George_George4-Sep-08 22:47

4-Sep-08 22:47

Thanks Nibu!

I want to find all possible exception which may be thrown from STL functions, for example, string.substr may throw out of range exception. But such information can not be found from MSDN. Do you have any reference documents?

regards,
George

Naveen4-Sep-08 20:10

Naveen

4-Sep-08 20:10

As you know that CString have functions for all the above things, I think refering to CString code will help you to understand the best methods.

nave

[OpenedFileFinder] [My Blog]

George_George4-Sep-08 20:11

4-Sep-08 20:11

Any non-MFC solutions? Smile | :)

regards,
George

Rajesh R Subramanian4-Sep-08 20:41

Rajesh R Subramanian

4-Sep-08 20:41

See here[^]

Also, see STL - some string utilities[^]

Many are stubborn in pursuit of the path they have chosen, few in pursuit of the goal - Friedrich Nietzsche

.·´¯`·->Rajesh<-·´¯`·.
[Microsoft MVP - Visual C++]

George_George4-Sep-08 21:39

Class initialization and memory allocation

4-Sep-08 21:39

Thanks Rajesh,

I want to find all possible exception which may be thrown from STL functions, for example, string.substr may throw out of range exception. But such information can not be found from MSDN. Do you have any reference documents? Smile | :)

regards,
George

Christian Flutcher4-Sep-08 19:11

Re: Class initialization and memory allocation [modified]

4-Sep-08 19:11

#include <iostream.h>
class Person
{
        string name;
        int age;
public:
        string GetName(void);
        int GetAge(void);
        Person(string personName,int personAge);
        Person(void);
};

int main()
{
        Person *person = new Person("Chris",30);
        cout << person->GetName() << endl;
        cout << person->GetAge() << endl;

        Person anotherPerson;
        cout << anotherPerson.GetName() << endl;
        cout << anotherPerson.GetAge() << endl;

        delete person;
        return 0;
}

string Person::GetName()
{
        return name;
}
int Person::GetAge()
{
        return age;
}
Person::Person(string personName,int personAge)
{
        name = personName;
        age = personAge;
}
Person::Person()
{
        name = "Unknown";
        age = 0;
}

I used to program using C# and learning C++ now. I have some doubts on the above shown program.

1 - Person anotherPerson is declared but not initialized. But still calls to anotherPerson.GetName() worked. How this is happening?

2 - Is there any difference when allocating memory for *person and anotherPerson?

3 - I know we should delete the pointer variables to claim memory. But AFAIK, there is no need to delete the anotherPerson variable. How it gets removed from memory?

_AnsHUMAN_ 4-Sep-08 19:27

_AnsHUMAN_

4-Sep-08 19:27

Christian Flutcher wrote:
1 - Person anotherPerson is declared but not initialized. But still calls to anotherPerson.GetName() worked. How this is happening?

The compiler provides a default constructor for the class. So when you create an object for the class the default constructor gets invoked and the object is initialized.

Christian Flutcher wrote:
2 - Is there any difference when allocating memory for *person and anotherPerson?

Yes. The memory is allocated from heap in case you use new (ie *person), otherwise it is allocated from stack.

Christian Flutcher wrote:
3 - I know we should delete the pointer variables to claim memory. But AFAIK, there is no need to delete the anotherPerson variable. How it gets removed from memory?

The memory allocated is returned to the stack once the object goes out of scope

Somethings seem HARD to do, until we know how to do them.
Wink | ;-)

_AnShUmAn_

modified on Friday, September 5, 2008 1:33 AM

Christian Flutcher4-Sep-08 19:40

4-Sep-08 19:40

Thanks

_AnShUmAn_ wrote:
Yes. The memory is allocated from heap in case you use new (ie *person), otherwise it is allocated from stack.

Well, so which one is the recommended practice? use pointer variables always and delete after usage or use the normal one which goes to stack?

Cedric Moonen4-Sep-08 19:57

Cedric Moonen

4-Sep-08 19:57

Depends really of the situation, sometimes you will need to use pointers so you don't have a choice. I tend to prefer using variables on the stack rather than on the heap when I can. Allocating/deallocating a lot of variables on the heap can lead to memory fragmentation which can be an issue if you tend to do it a lot. Furthermore, the cost (in time) of creating an object on the heap is a bit higher than creating an object on the stack.

Cédric Moonen
Software developer

Charting control [v1.5]
OpenGL game tutorial in C++

Christian Flutcher4-Sep-08 20:20

4-Sep-08 20:20

Cedric Moonen wrote:
Allocating/deallocating a lot of variables on the heap can lead to memory fragmentation which can be an issue if you tend to do it a lot

Are there any rules which should be considered when instantiating objects? How do you decide where the object should go? I am bit confused Confused | :confused:

Cedric Moonen4-Sep-08 20:27

Cedric Moonen

4-Sep-08 20:27

No, there's no rule for this but in most of the cases, it's not a big problem if you allocate a variable on the heap or on the stack. One point to remember is that variables on the stack will be destroyed when they go out of scope. So, if you have a variable which is local to a function, this variable will be destroyed when the function exits.
Or if you want a simple rule: try to allocate variables on the stack when you can.

Cédric Moonen
Software developer

Charting control [v1.5]
OpenGL game tutorial in C++

Christian Flutcher4-Sep-08 20:29

4-Sep-08 20:29

Thanks Cedric. Your help is much appreciated.