由“ can i get a char* , please?"看起：

Just barely. OO.o has at least six string wrappers, although the C implementations are of little interest:

• rtl_String — sal/inc/rtl/string.h
  "Normal" string plus reference counting. rtlstring->buffer is useful, as is rtlstring->length. This object encapsulates an generic 8bit string - of unknown encoding. Feel free to treat rtlstring->buffer as your beloved char *. If you really want to look at the implementation of some rtl_String function and lxr nor grep can help you, have a look at sal/rtl/source/strtmpl.c.

• OString — sal/inc/rtl/string.hxx
  Simply a rtl_String wrapped inside a class; you can use ostring.pData to get at the rtl_String (it‘s public). OString has reasonably useful methods for if you need them.

• rtl_uString — sal/inc/rtl/ustring.h
  "Normal" Unicode string, similar to rtl_String, and refcounted as well. However, this one always comes in UCS-2 encoding, presumably to be compatible with Java‘s questionable choices. See rtl_String above to find where the implementation of some rtl_uStringfunctions is hidden.

• OUString — sal/inc/rtl/ustring.hxx
  An rtl_uString wrapped inside a class. This is what most of the OO.o code uses to pass strings around. To convert an OString to an OUString it is necessary to specify the character set of the OString see; sal/inc/rtl/textenc.h — the only interesting case is RTL_TEXTENCODING_UTF8

• String — tools/inc/string.hxx
  This is an obsolete string class, aliased to ‘UniString‘. It has a number of limitations such as a 64k length limit. You can have the buffer with GetBuffer(), but it‘s Utf-16 encoded.

A couple of conversion functions are really useful here, particularly:
rtl::OString aOString = ::rtl::OUStringToOString (aOUString, RTL_TEXTENCODING_UTF8); 
And the reverse:
rtl::OUString aOUString = ::rtl::OStringToOUString (aOString, RTL_TEXTENCODING_UTF8);

If you just want to programattically print out a string for debugging purposes you probably want define a macro like :
#define CHAR_POINTER(THE_OUSTRING) ::rtl::OUStringToOString (THE_OUSTRING, RTL_TEXTENCODING_UTF8).pData->buffer 
and use it like :
printf ( "SvXMLNamespaceMap::AddIfKnown : %s / %s\n", CHAR_POINTER(rPrefix), CHAR_POINTER(rName) );. 
For the obsolete String class, aliased UniString, it‘s like :
printf ( "rGrfName : %s\n", ByteString( rGrfName, RTL_TEXTENCODING_UTF8).GetBuffer() );

To print the value of rtl::OUString directly in the debugger, you can use dbg_dump(). It is intended to be called interactively from the debugger, in both debug and non-debug builds of OOo. You can see the definition in sal/rtl/source/debugprint.cxx.

Some code snippets about manipulating those objects can be found on the codesnippets service page : [1]

原文链接：https://wiki.openoffice.org/wiki/Hacking#Can_I_get_a_char_.2A.2C_please.3F

继续看sal模块源码，摘录：

/********************************************************************************/
/* Data types
*/

/* Boolean */
typedef unsigned char sal_Bool;
# define sal_False ((sal_Bool)0)
# define sal_True ((sal_Bool)1)

/* char is assumed to always be 1 byte long */
typedef signed char sal_Int8;
typedef unsigned char sal_uInt8;

#if SAL_TYPES_SIZEOFSHORT == 2
typedef signed short sal_Int16;
typedef unsigned shortsal_uInt16;//2字节
#else
#error "Could not find 16-bit type, add support for your architecture"
#endif

typedef charsal_Char;//1字节

#if ( defined(SAL_W32) && !defined(__MINGW32__) )
typedef wchar_tsal_Unicode;
#else
#define SAL_UNICODE_NOTEQUAL_WCHAR_T
typedef sal_uInt16 sal_Unicode;//2字节
#endif

“Normal”string, 8-bit string, unknown encoding 字符串操作c函数

/** The implementation of a byte string.

@internal
*/
typedef struct _rtl_String
{
oslInterlockedCount refCount; /* opaque */
sal_Int32 length;
sal_Char buffer[1];
} rtl_String;//1字节，8bit string

rtlstring wrapped inside a class openoffice的字符串类OString

class OString
{
public:
/** @internal */
rtl_String * pData;

usc-2 encoding 一组对unicode字符串操作的c函数

/** The implementation of a Unicode string.

@internal
*/
typedef struct _rtl_uString
{
oslInterlockedCount refCount; /* opaque */
sal_Int32 length;
sal_Unicode buffer[1];
} rtl_uString;

rtl_ustring wrapped in a class openoffice的OUString类，封装rtl_ustring的c++类

class OUString
{
public:
/** @internal */
rtl_uString * pData;