PROBLEM: why can't auto-covert char [10][10] into char **

[Wisdo]

Hi All,

char [10][10] to char ** is compile error. why?

if i hava a string array. yes. it's not safe and it's better to use
vector<stringin stead.

but my point is the language feature.

char sex[2][128] = {"Male", "Female" };

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

Regards
-Wisdo

[tolgaceylanus]

void print(char (*p)[128], int len)

definition should fix your problem. Functions that have 2 dimensional
arrays
as arguments need a hint to be able to offset the arrays properly. This
is
because these are arrays of arrays actually.

Hope this helps,

Tolga Ceylan

[Daniel T.]

Wisdo <wi***@hf.webex .comwrote:

Hi All,

char [10][10] to char ** is compile error. why?

if i hava a string array. yes. it's not safe and it's better to use
vector<stringin stead.

but my point is the language feature.

char sex[2][128] = {"Male", "Female" };

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

Yes, char[][] is not the same as a char**. 'sex' isn't a pointer to a
pointer to a char.

[Jim Langston]

"Wisdo" <wi***@hf.webex .comwrote in message
news:ec******** **@news.yaako.c om...

Hi All,

char [10][10] to char ** is compile error. why?

if i hava a string array. yes. it's not safe and it's better to use
vector<stringin stead.

but my point is the language feature.

char sex[2][128] = {"Male", "Female" };

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

Regards
-Wisdo

Because char [10][10] is not an array of pointers, it is a two dimentional
array of characters.
The memory is allocated and used about the same way as char [100] and you
can test that yourself.

This prints out Male and Female twice. Pick the one you like best.

void print( const char p[][128], const int length )
{
for ( int i = 0; i < length; ++i )
std::cout << &p[i][0] << std::endl;
}

void print2( const char* p, const int width, const int length )
{
for ( int i = 0; i < length; ++i )
std::cout << &p[width * i] << std::endl;
}

int main()
{
char sex[2][128] = {"Male", "Female" };
print( sex, 2 );
print2( reinterpret_cas t<const char *>( sex ), 128, 2 );
}

[Frederick Gotham]

Wisdo posted:

Hi All,

char [10][10] to char ** is compile error. why?

Type mismatch, both before and after the array-to-pointer decay.

if i hava a string array. yes. it's not safe and it's better to use
vector<stringin stead.

Incorrect -- arrays yield well-defined behaviour in C++.

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

Your speech is unintelligible.

Here's some sample code:

#include <cstddef>
#include <cassert>
#include <iostream>

using std::cout;
using std::size_t;

#define restrict /* Nothing */
#define nullptr 0 /* Until next standard */

size_t const buflen = 64;

void PrintNullTermin atedArrayOfPoin tersToStrings(c har const *const restrict
*restrict p)
{
assert(p);
assert(*p);

do cout << *p++ << '\n';
while(*p);
}

void PrintNullTermin atedArrayOfStri ngs(char const *restrict p)
{
assert(p);
assert(*p);

do cout << p << '\n';
while(*(p += buflen));
}

int main()
{
char const *const restrict names1[] = {
"Michael","John ","Philip","Bar ry","Thomas",
"Luke","Owen"," Richard","Keith ",nullptr};

char const names2[][buflen] = {
"Michael","John ","Philip","Bar ry","Thomas",
"Luke","Owen"," Richard","Keith ", {0} };

PrintNullTermin atedArrayOfPoin tersToStrings(n ames1);

PrintNullTermin atedArrayOfStri ngs(*names2);
}

--

Frederick Gotham

[Greg Comeau]

In article <ec**********@n ews.yaako.com>, Wisdo <wi***@hf.webex .comwrote:

>Hi All,

char [10][10] to char ** is compile error. why?

if i hava a string array. yes. it's not safe and it's better to use
vector<stringi nstead.

but my point is the language feature.

char sex[2][128] = {"Male", "Female" };

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

The problem is that you do not have an array of pointers,
you have an array or array's, so something like sex[1][2]
has to get to the right group of [128]'s. It's not sure
what you want here, but perhaps you want to pass each
sex[i] and accept a char * instead.
--
Greg Comeau / 20 years of Comeauity! Intel Mac Port now in alpha!
Comeau C/C++ ONLINE == http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

[Greg Comeau]

In article <ec**********@p anix2.panix.com >,
Greg Comeau <co****@comeauc omputing.comwro te:

>In article <ec**********@n ews.yaako.com>, Wisdo <wi***@hf.webex .comwrote:

>>char [10][10] to char ** is compile error. why?

if i hava a string array. yes. it's not safe and it's better to use
vector<string instead.

but my point is the language feature.

char sex[2][128] = {"Male", "Female" };

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

The problem is that you do not have an array of pointers,
you have an array or array's, so something like sex[1][2]
has to get to the right group of [128]'s. It's not sure
what you want here, but perhaps you want to pass each
sex[i] and accept a char * instead.

Oops if not obvious "array or arrays" should say "array of arrays"
--
Greg Comeau / 20 years of Comeauity! Intel Mac Port now in alpha!
Comeau C/C++ ONLINE == http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

[Noah Roberts]

to***********@y ahoo.com wrote:

void print(char (*p)[128], int len)

Yet another reason to just use the standard classes to your advantage
is that rather convoluted and entirely necissary definition.

[Pierre Barbier de Reuille]

Wisdo wrote:

Hi All,

char [10][10] to char ** is compile error. why?

if i hava a string array. yes. it's not safe and it's better to use
vector<stringin stead.

but my point is the language feature.

char sex[2][128] = {"Male", "Female" };

void print(char **p, int len) {
// print all sex
}

print(sex, 128); // <--- this cause compile error.

Is any issue to make the language forbiden this covertion?

Regards
-Wisdo

Simply, one (IMHO) convenient way to implement the print function is to
use template:

#include <iostream>

using namespace std;

template <size_t N>
void print(char p[][N], int len)
{
for(int i = 0 ; i < len ; ++i)
{
cout << p[i] << endl;
}
}

int main()
{
char sex[2][128] = {"Male", "Female" };
print(sex, 2);
return 0;
}

Pierre

[Frederick Gotham]

Noah Roberts posted:

>void print(char (*p)[128], int len)

Yet another reason to just use the standard classes to your advantage
is that rather convoluted and entirely necissary definition.

I see nothing convoluted about it, but then again I'm not afraid of C++.

--

Frederick Gotham