two dimensional array initialization

[George_George]

Thanks toxcct, I need to use C other than C++. What do you think is the best solution in C? regards, George

[George_George]

Cool! regards, George

[codeII]

Dynamic you can do it something like this: int nNmbOfStrings = 2; int nI; LPTSTR* pArr = new LPTSTR[ nNmbOfStrings ]; pArr[ 0 ] = new TCHAR[ _tcslen( _T("hello") ) + 1 ]; pArr[ 1 ] = new TCHAR[ _tcslen( _T("world") ) + 1 ]; _tcscpy( pArr[ 0 ], _T("hello") ); _tcscpy( pArr[ 1 ], _T("world") ); //deletion: for ( nI = 0; nI < nNmbOfStrings; nI++ ) { delete [] pArr[ nI ]; pArr[ nI ] = NULL; } delete [] pArr; pArr = NULL;

[George_George]

Thanks koos, It works but a little complex. regards, George

[codeII]

Yep, It only makes sence when you dynamically want assign/reassign an array. //f.i. reassign string 2 (before deletion!): delete [] pArr[ 1 ]; pArr[ 1 ] = new TCHAR[ _tcslen( _T("Every body") ) + 1 ]; _tcscpy( pArr[ 1 ], _T("Every body") ); Regards, Koos

[Michael Dunn]

If you want to stick with fixed-sized array bounds, you have to specify all bounds except the first. That's why [][] is an error but [][64] is OK.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ

[Michael Dunn]

Keep in mind that George's solution is not the same as your original code. Most notably, you shouldn't write to any of the memory occupied by the strings, whereas with regular arrays, it's always safe to write to that memory.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ

[George_George]

Thanks koos, I am aware that your method has advantage. regards, George

[George_George]

Thanks Mike, Could you explain from compiler internal point of view why I need to provide the innermost size, why I can not make it empty (e.g. [][])? I think it must break some rules or make compiler confused to make proper decision to generate object code, but I can not find why. regards, George

[George_George]

Thanks Mike, 1. Why his solution is not the same as mine? 2. How memory corruption will occur? Could you let me know an example please? I am using the array as constant string, so I can not imagine a case which will cause memory corruption. regards, George

[Michael Dunn]

char s1[] = "foo";
char* s2 = "bar";
strcpy ( s1, "aaa" ); // ok
strcpy ( s2, "bbb" ); // not ok

The memory pointed to by s2 should be treated as read-only.

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ Dunder-Mifflin, this is Pam.

[Michael Dunn]

char s1[4] = "cat";
char s2[] = "dog";

In both of those cases, the array size is 4. The compiler can deduce the size of s2 from the initializer string, which is 4 chars long.

char* s3[2] = { "hello", "bob" };
char* s4[] = { "code", "project" };

Here, the arrays contain char*. Again, the compiler can deduce the size of s4 because the initializer has two char*s. Now make it a 2-D array (I'll switch to ints since the initializer syntax is more precise)

int i5[5][2] = { {1,2,3,4,5}, {6,7,8,9,10} };

i5 is an array of two int[5] arrays. Now if I did this:

int i6[5][] = { {1,2,3,4,5}, {6,7,8,9,10}, {0,2,4,6,8} };

Since I used three int[5] arrays in the initializer, the compiler deduces that i6 is int[5]**[3]**. (BTW I just realized that my earlier post was wrong, it's the last dimension that you can leave out, not the first.)

--Mike-- Visual C++ MVP :cool: LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ Dunder-Mifflin, this is Pam.

[George_George]

Good point! Thanks Mike! I have not noticed this point before. regards, George

[George_George]

Hi Mike, The code, int i6[5][] = { {1,2,3,4,5}, {6,7,8,9,10}, {0,2,4,6,8} }; will not compile. You should use, int i6[][5] = { {1,2,3,4,5}, {6,7,8,9,10}, {0,2,4,6,8} }; or int i6[3][5] = { {1,2,3,4,5}, {6,7,8,9,10}, {0,2,4,6,8} }; regards, George