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string to char*

Started by Peaceman Jun 11, 2002 at 10:40 AM 8 replies 400+ views

Original Post

Jun 11, 2002 at 10:40 AM

Hi guys, I need to convert a string(STL) to a normal char * or if it helps just to a char[128]. I''d appreciate some help on this one, as I couldn''t find a conversionroutine from string to char. thx

IDispatch

Jun 11, 2002 at 10:44 AM

This should do it:

sMyString.c_str();

DerekSaw

Jun 11, 2002 at 10:46 AM


...
std::string abc = "Some string";
char *p;

p = abc.c_str();
//or
p = abc.data();

[edited by - DerekSaw on June 11, 2002 11:49:01 AM]

Peaceman

Author

Peaceman

Jun 11, 2002 at 11:02 AM

thx for your fast replies

Peaceman

Author

Peaceman

Jun 11, 2002 at 11:09 AM

If I use this code:

...
std::string abc = "Some string";
char *p;

p = abc.c_str();
//or
p = abc.data();

I get "error C2440: ''='' : cannot convert from ''const char *'' to ''char *''"

Why?

SabreMan

127

SabreMan

Jun 11, 2002 at 11:18 AM

Because c_str() returns a const char*, of course. If you are passing to a legacy API, and that API modifies the c-string, then you will need to make a copy. If the API does not modify the c-string, then you can perform a const_cast.

siaspete

Jun 11, 2002 at 11:18 AM

Are you trying to copy the string to an array of chars, or get a pointer to it?

If you''re trying to copy it, you must do something like this...

char array[100];
strcpy (array, str.c_str ());

If you''re trying to get a pointer to it, I recommend against it, as the pointer you get is not necessarily going to be valid for any length of time.

Helpful links:
How To Ask Questions The Smart Way | Google can help with your question | Search MSDN for help with standard C or Windows functions

Atavist

Jun 11, 2002 at 11:27 AM

Usually you would use abc.c_str() to compare against another string, and being const char* is best for a compare.
If you want to make a seperate copy of the string, you do just that you make a copy:


std::string abc = "Some string";
char *p;
int len;

len = abc.length();
p = new char[len+1];
strcpy(p,abc.c_str());

//later on make sure to
delete [] p;

Now you have a copy thats independant of abc.

edit: love these simple questions

its easy for lots of people to answer

[edited by - atavist on June 11, 2002 12:29:43 PM]

DerekSaw

Jun 11, 2002 at 8:01 PM

quote:
Original post by Peaceman
If I use this code:

...
std::string abc = "Some string";
char *p;

p = abc.c_str();
//or
p = abc.data();

I get "error C2440: ''='' : cannot convert from ''const char *'' to ''char *''"

Why?

Oooops... forgot that it return const char *

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