C++ Borland char * and strcpy

Question

char *dum[32];
strcpy(&dum,InstList->Lines->Text.c_str());

InstList is a TMemo of C++ Builder

Why am I getting this error?

[C++ Error] emulator.cpp(59): E2034 Cannot convert 'char * *' to 'char *' Full parser context emulator.cpp(56): parsing: void _fastcall TMain::Button1Click(TObject *)

score 2 · Answer 1 · answered Oct 29 '11 at 11:49

char *dum[32];

is an array of length 32, each element being a char*. I guess you meant to write

char dum[32];

This is an array of 32 char and you can then write:

strcpy(dum, InstList->Lines->Text.c_str());

Make sure, of course, InstList->Lines->Text is not so big that it overflows your buffer.

Of course, I'm not sure why you would need to use C strings in a C++ program.

Yahia · Answer 2 · 2011-10-29T21:27:44.077

2

You either use (prone to serious security problem called buffer overflow)

char dum[32];
strcpy(dum,InstList->Lines->Text.c_str());

OR (much better since it works with any length without being prone to a serious security problem called buffer overflow)

// C style
// char *dum = malloc(strlen(InstList->Lines->Text.c_str())+1); 

// BCB style...
char *dum = malloc(InstList->Lines->Text.Length()+1);  

// BEWARE: AFTER any malloc you should check the pointer returned for being NULL

strcpy(dum,InstList->Lines->Text.c_str());

EDIT - as per comments:

I am assuming that you are using an older BCB version which still has AnsiString - if this is on a newer version UnicodeString then the code could lead to "strange results" since unicode string take up multiple bytes per character (depending on the encoding etc.).

edited Oct 29 '11 at 21:27

answered Oct 29 '11 at 11:51

Yahia

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Good points, but no need even to use `strlen` since `InstList->Lines->Text` comes with a length property for sure. Not sure on the C++ Builder syntax mind you. – David Heffernan Oct 29 '11 at 11:52
@DavidHeffernan Last time I used C++ Builder is several years ago... looked it up... – Yahia Oct 29 '11 at 11:55
According to the docs, `Text` is `System::UnicodeString` and you would write `Length(System::UnicodeString)` from Delphi, I assume that C++ Builder is the same. `Text` is dynamically generated from the contents of the Windows EDIT control that is behind the TMemo. I'd probably read it out into a `System::UnicodeString` variable first. One can only wonder where C strings come into the equation. – David Heffernan Oct 29 '11 at 11:57
@DavidHeffernan you are right for the current versions... but for example C++ Builder 6(!) has this as `AnsiString` defined... unbelievable but V 6 is still in use... when I saw the C string handling I thought of the old versions, otherwise this code would do no good... – Yahia Oct 29 '11 at 12:00
@DavidHeffernan checked the docs... `System::UnicodeString` would return `wchar_t *` as a result of `c_str()`... given the error message the OP posted this seems to be an older version with `AnsiString`... – Yahia Oct 29 '11 at 12:04
Yeah, you're right. I didn't know you could do `::Length()` and `::c_str()` on a C++Builder `AnsiString` or indeed `UnicodeString`. None of that available for us Delphi users! There were would write `Length(str)` and `PChar(str)`. Anyway, I think we've got this Q covered. – David Heffernan Oct 29 '11 at 12:08

score 1 · Answer 3 · answered Oct 29 '11 at 11:49

1

char dum[32];   
strcpy(dum,InstList->Lines->Text.c_str());

answered Oct 29 '11 at 11:49

Alex F

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score 1 · Answer 4 · edited Oct 29 '11 at 12:08

1

Do not use char* use String or std::string instead and if you need a pointer to your string for some reason just take this from your string object.

String myString = InstList->Lines->Text;
myString.c_str();

edited Oct 29 '11 at 12:08

David Heffernan

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answered Oct 29 '11 at 12:01

AlexTheo

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C++ Borland char * and strcpy

4 Answers4