Pointer to Pointer

[howa]

Hi,

How to manually add an array of string, which is pointer by a pointer,
e.g.

char **str;

// add "this", "is", "a", "test" one by one into the 2d array?

thanks.

[Bart]

howa wrote:

Hi,

How to manually add an array of string, which is pointer by a pointer,

In C++ a string means the std::string class:

#include <string>

std::string mystring = "this is a string";

What you probably mean is a C-style array of chars, but it is
recommended that you avoid them in C++.

char **str;

// add "this", "is", "a", "test" one by one into the 2d array?

You have a pointer, not a 2D array. It is very, VERY wrong to think of
double-pointers as arrays.

Anyway, you should use a standard vector of strings instead:

#include <vector>
#include <string>

std::vector<std::stringmystrings;
mystrings.push_back("some string");

mystrings[0]; // <-- you access the vector just like any array

Regards,
Bart.

[howa]

Bart 寫�：

howa wrote:

Hi,

How to manually add an array of string, which is pointer by a pointer,

In C++ a string means the std::string class:

#include <string>

std::string mystring = "this is a string";

What you probably mean is a C-style array of chars, but it is
recommended that you avoid them in C++.

char **str;

// add "this", "is", "a", "test" one by one into the 2d array?

You have a pointer, not a 2D array. It is very, VERY wrong to think of
double-pointers as arrays.

Anyway, you should use a standard vector of strings instead:

#include <vector>
#include <string>

std::vector<std::stringmystrings;
mystrings.push_back("some string");

mystrings[0]; // <-- you access the vector just like any array

Regards,
Bart.

is it possible to create dynamically using char* ?

just like the int main(char **argv) ?

thanks.

[Pete Becker]

Bart wrote:

howa wrote:

>Hi,

How to manually add an array of string, which is pointer by a pointer,

In C++ a string means the std::string class:

#include <string>

std::string mystring = "this is a string";

Not when the text clearly refers to a C-style string.

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

[Pete Becker]

howa wrote:

>
is it possible to create dynamically using char* ?

just like the int main(char **argv) ?

Yup.

typedef char *str; // less confusing
str *mystr; // dynamically allocated array
mystr = new str[whatever_you_need];
for (int i = 0; i < whatever_you_need; ++i)
str[i] = new char[whatever_i_needs];

The bookkeeping can be tricky, though, so be careful.

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

[Default User]

howa wrote:

Hi,

How to manually add an array of string, which is pointer by a pointer,
e.g.

char **str;

// add "this", "is", "a", "test" one by one into the 2d array?

thanks.

Sounds like homework. What do you have so far? What confuses you? Do
you know what dynamic memory allocation is, and how to do it?

Crack your book and get to it!


Brian

[Bart]

Pete Becker napisal(a):

Bart wrote:

howa wrote:

How to manually add an array of string, which is pointer by a pointer,

In C++ a string means the std::string class:

Not when the text clearly refers to a C-style string.

When a poster seems confused and is obviously new to the language I
feel obligated to point them in the right direction. I still maintain
that in the context of C++ the term 'string' by itself should be used
only for std::string and that a more qualified term should be used to
refer to C-style strings.

Regards,
Bart.

[Bart]

howa napisal(a):

is it possible to create dynamically using char* ?

just like the int main(char **argv) ?

That's not a correct declaration of main. And yes, you can allocate it
dynamically, but the question is why? Is this homework? If it's not,
then you should use std::string. Even the argv parameter of main should
not be manipulated as is, but used to initialize a std::string instead.

Regards,
Bart.

[Pete Becker]

Bart wrote:

Pete Becker napisal(a):

>Bart wrote:

>>howa wrote:
How to manually add an array of string, which is pointer by a pointer,
In C++ a string means the std::string class:

Not when the text clearly refers to a C-style string.

When a poster seems confused and is obviously new to the language I
feel obligated to point them in the right direction. I still maintain
that in the context of C++ the term 'string' by itself should be used
only for std::string and that a more qualified term should be used to
refer to C-style strings.

I see. You point them in the right direction by stating your opinion as
if it was a universal truth.

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

[Pete Becker]

Bart wrote:

Even the argv parameter of main should
not be manipulated as is, but used to initialize a std::string instead.

There's nothing wrong with indexing into argv. Creating unnecessary
objects just bloats your code.

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

[Bart]

Pete Becker wrote:

Bart wrote:

Even the argv parameter of main should
not be manipulated as is, but used to initialize a std::string instead.

There's nothing wrong with indexing into argv. Creating unnecessary
objects just bloats your code.

Feel free to call a single instance in your main function "bloat" if
you like. Some prefer the added convenience.

Regards,
Bart.

[howa]

Pete Becker 寫�：

howa wrote:

is it possible to create dynamically using char* ?

just like the int main(char **argv) ?

Yup.

typedef char *str; // less confusing
str *mystr; // dynamically allocated array
mystr = new str[whatever_you_need];
for (int i = 0; i < whatever_you_need; ++i)
str[i] = new char[whatever_i_needs];

The bookkeeping can be tricky, though, so be careful.

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

thanks!