Ogre::IdString Struct Reference

Hashed string. More...

#include <OgreIdString.h>

Public Member Functions
	IdString ()
	IdString (const char *string)
	IdString (const std::string &string)
	IdString (uint32 value)
std::string	getFriendlyText () const
	Returns "[Hash 0x0a0100ef]" strings in Release mode, readable string in debug.
void	getFriendlyText (char *outCStr, size_t stringSize) const
	C String version.
std::string	getReleaseText () const
	Always returns "[Hash 0x0a0100ef]" strings in any mode.
void	getReleaseText (char *outCStr, size_t stringSize) const
	C String version. Zero allocations. See getFriendlyText.
bool	operator!= (IdString idString) const
IdString	operator+ (IdString idString) const
void	operator+= (IdString idString)
bool	operator< (IdString idString) const
bool	operator== (IdString idString) const

Public Attributes
uint32	mHash

Static Public Attributes
static const uint32_t	Seed = 0x3A8EFA67

Detailed Description

Hashed string.

An IdString is meant to be passed by value rather than by reference since in Release mode it's just an encapsulated integer. The default implementation uses a 32-bit uint. A hash = 0 is the default initialization, and assumed by Ogre to mean an IdString is empty or unspecified.

Note that IdString("") != IdString(0) != IdString() The latter indicates mHash == 0 (the default initialization). While the first one will hash the empty string "", and the second will attempt to hash the number 0, producing up to three possible outputs.

IdStrings convert regular String to hashes AND ARE DESTRUCTIVE. This means that you may no longer recover the real string it was constructed from. When the original data is not available getFriendlyText returns [Hash 0x0a0100ef] (in the example that mHash = 0x0a0100ef)* In debug mode (OGRE_DEBUG_MODE is defined), IdStrings try to maintain a copy of the original string for two purposes:

1. Easy debugging: Reading "Texture/diffuse.png" is much nicer than "0x0a0100ef"
2. Hash collision: If Ogre finds two IdStrings are identical but their original strings are not, an assertion will trigger indicating a collision has been found. Note that this isn't foolproof. Note: When IdString( uint32 ) was used to hash an integer, getFriendlyText will return "[Value 0x1234567]"

IdStrings can be concatenated: IdString( "Hello." ) + IdString( " How are you?" ) produc a new IdString, but please note that it may not be the same as doing IdString( "Hello. How are you?" ) depending on the hashing function used (by default, we use MurmurHash3,

See also

OGRE_HASH_FUNC)

Remarks

Hash collision detection isn't foolproof because we keep a fixed string copy of the original string. If the original string is too long, it will be truncated and there is an extremely low possibility that their truncation becomes the same string, and their hashes also become equal, when the original strings were not. i.e. VeryLooooooong/String and UltraaaaaLoong/String could both become "/String" and happen to also hash to the same number.

In practice we truncate to 32 bytes. If your fear this is too little for you and also fear about collisions, increase @OGRE_DEBUG_STR_SIZE

Author

Matias N. Goldberg

Version

1.0

Constructor & Destructor Documentation

IdString() [1/4]

Ogre::IdString::IdString ( )

inline

IdString() [2/4]

Ogre::IdString::IdString ( const char *  string )

inline

References mHash, OGRE_COPY_DEBUG_STRING, OGRE_HASH_FUNC, and Seed.

IdString() [3/4]

Ogre::IdString::IdString ( const std::string &  string )

inline

References mHash, OGRE_COPY_DEBUG_STRING, OGRE_HASH_FUNC, and Seed.

IdString() [4/4]

Ogre::IdString::IdString ( uint32  value )

inline

References mHash, OGRE_COPY_DEBUG_STRING, OGRE_HASH_FUNC, and Seed.

Member Function Documentation

getFriendlyText() [1/2]

std::string Ogre::IdString::getFriendlyText ( ) const

inline

Returns "[Hash 0x0a0100ef]" strings in Release mode, readable string in debug.

References getReleaseText().

getFriendlyText() [2/2]

void Ogre::IdString::getFriendlyText ( char *  outCStr, size_t  stringSize  ) const

inline

C String version.

Zero allocations.

Parameters

outCStr	C String to store the string.
stringSize	Size of of outCStr. Recommended size: OGRE_DEBUG_STR_SIZE

References getReleaseText().

getReleaseText() [1/2]

std::string Ogre::IdString::getReleaseText ( ) const

inline

Always returns "[Hash 0x0a0100ef]" strings in any mode.

References mHash, and OGRE_HASH_BITS.

Referenced by getFriendlyText(), and getFriendlyText().

getReleaseText() [2/2]

void Ogre::IdString::getReleaseText ( char *  outCStr, size_t  stringSize  ) const

inline

C String version. Zero allocations. See getFriendlyText.

References mHash, and OGRE_HASH_BITS.

operator!=()

bool Ogre::IdString::operator!= ( IdString  idString ) const

inline

References mHash.

operator+()

IdString Ogre::IdString::operator+ ( IdString  idString ) const

inline

operator+=()

void Ogre::IdString::operator+= ( IdString  idString )

inline

References mHash, OGRE_APPEND_DEBUG_STRING, OGRE_HASH_FUNC, and Seed.

operator<()

bool Ogre::IdString::operator< ( IdString  idString ) const

inline

References mHash.

operator==()

bool Ogre::IdString::operator== ( IdString  idString ) const

inline

References mHash.

Member Data Documentation

mHash

uint32 Ogre::IdString::mHash

Referenced by IdString(), IdString(), IdString(), getReleaseText(), getReleaseText(), operator!=(), operator+=(), operator<(), and operator==().

Seed

const uint32_t Ogre::IdString::Seed = 0x3A8EFA67

static

Referenced by IdString(), IdString(), IdString(), and operator+=().

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The documentation for this struct was generated from the following file:

• OgreIdString.h