SomeClass::SomeClassConstructor()
{
string = new char[ 50 ];
}
SomeClass::SomeClassgetString()
{
if ( string == 0 )
cout << "String is empty";
else
cout << string << endl;
}
empty strings....
Author
you can not test if a string is empty by comparing it 0. Try using the int strlen(char*) function. example:
for a little more of an explination:
when you define a char* and set it to new, you give that variable (pointer) a value which is the memory adress of that new memory. when you do if(str == 0), you are testing to see if that memory's address is 0.
Hopefully that made some sence... You might want to do some reasearch on pointers for more info.
Dwiel
if(strlen(str) == 0) // str is emptyfor a little more of an explination:
when you define a char* and set it to new, you give that variable (pointer) a value which is the memory adress of that new memory. when you do if(str == 0), you are testing to see if that memory's address is 0.
Hopefully that made some sence... You might want to do some reasearch on pointers for more info.
Dwiel
Author
hmmm. I tried that, but it doesn't work....
this is what I have:
void viewChar( PlClient &seeObj )
{
if ( strlen( seeObj.plName ) == 0 )
cout << "A name is not assigned\n";
else
cout << seeObj.plName << endl;
}
This is what happens:
this is what I have:
void viewChar( PlClient &seeObj )
{
if ( strlen( seeObj.plName ) == 0 )
cout << "A name is not assigned\n";
else
cout << seeObj.plName << endl;
}
This is what happens:
I don't know how it works in C++, but in C when you declare a variable, it always hold something. The best way to ensure a string to be empty is to assign an empty string("") or NULL.
Author
ahh. finally I got it. I declared plName as a NULL like:
*plName = NULL;
if I left it as
plName = NULL;
would that mean I'm telling plName to have no address? but when I do: *plName = NULL, I'm telling it to be an empty string?
*plName = NULL;
if I left it as
plName = NULL;
would that mean I'm telling plName to have no address? but when I do: *plName = NULL, I'm telling it to be an empty string?
For one thing, after you allocate new memory (with "new char[50]" in your case), the contents are not zero; they're just random garbage. For another, even if the string was empty, the easiest way to check is this:
Note that this assumes 'string' has been allocated. If, on the other hand, the string pointer is NULL (not allocated), which is not the same as being a valid, empty, string, then you'd use your original code "string == 0".
Anyway, after you create the string, add this:
That sets the first character to 0. Strings are null-terminated so calling cout on it now will print nothing; it's an empty string.
if( string[0] == 0 ) cout << "string is empty" << endl;Note that this assumes 'string' has been allocated. If, on the other hand, the string pointer is NULL (not allocated), which is not the same as being a valid, empty, string, then you'd use your original code "string == 0".
Anyway, after you create the string, add this:
string[0] = 0;That sets the first character to 0. Strings are null-terminated so calling cout on it now will print nothing; it's an empty string.
Quote:Original post by TheOne1
ahh. finally I got it. I declared plName as a NULL like:
*plName = NULL;
Which, if plName hasn't been allocated yet, would usually cause a crash, or a memory error that causes the program to crash later on.
Quote:
if I left it as
plName = NULL;
would that mean I'm telling plName to have no address?
Yes.
Quote:but when I do: *plName = NULL, I'm telling it to be an empty string?
Yes, that's the same as saying 'plName[0] = NULL', but this only works if the string has already been assigned memory.
Quote:Original post by TheOne1
This is what happens:
Simple, the memory you allocate is not initialised to zero and contains random gibberish. Add a "strcpy (plName, "");" to the constructor.
Better yet, simply use std::string, as suggested by Zahlman.
This topic is closed to new replies.
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