CnC Generals AsciiString

AsciiString.cpp

void AsciiString::ensureUniqueBufferOfSize(int numCharsNeeded, Bool preserveData, const char* strToCopy, const char* strToCat)
{
	validate();

	if (m_data &&
			m_data->m_refCount == 1 &&
			m_data->m_numCharsAllocated >= numCharsNeeded)
	{
		// no buffer manhandling is needed (it's already large enough, and unique to us)
		if (strToCopy)
			strcpy(m_data->peek(), strToCopy);
		if (strToCat)
			strcat(m_data->peek(), strToCat);
		return;
	}

	int minBytes = sizeof(AsciiStringData) + numCharsNeeded*sizeof(char);
	if (minBytes > MAX_LEN)
		throw ERROR_OUT_OF_MEMORY;

	int actualBytes = TheDynamicMemoryAllocator->getActualAllocationSize(minBytes);
	AsciiStringData* newData = (AsciiStringData*)TheDynamicMemoryAllocator->allocateBytesDoNotZero(actualBytes, "STR_AsciiString::ensureUniqueBufferOfSize");
	newData->m_refCount = 1;
	newData->m_numCharsAllocated = (actualBytes - sizeof(AsciiStringData))/sizeof(char);
#if defined(_DEBUG) || defined(_INTERNAL)
	newData->m_debugptr = newData->peek();	// just makes it easier to read in the debugger
#endif

	if (m_data && preserveData)
		strcpy(newData->peek(), m_data->peek());
	else
		newData->peek()[0] = 0;

	// do these BEFORE releasing the old buffer, so that self-copies
	// or self-cats will work correctly.
	if (strToCopy)
		strcpy(newData->peek(), strToCopy);
	if (strToCat)
		strcat(newData->peek(), strToCat);

	releaseBuffer();
	m_data = newData;

	validate();
}

AsciiString.h

class AsciiString
{
private:
	
	// Note, this is a Plain Old Data Structure... don't
	// add a ctor/dtor, 'cuz they won't ever be called.
	struct AsciiStringData
	{
#if defined(_DEBUG) || defined(_INTERNAL)
		const char* m_debugptr;	// just makes it easier to read in the debugger
#endif
		unsigned short	m_refCount;						// reference count
		unsigned short	m_numCharsAllocated;  // length of data allocated
		// unsigned int m_padding;
		// char m_stringdata[];

		inline char* peek() { return (char*)(this+1); }
	};

	#ifdef _DEBUG
	void validate() const;
	#else
	inline void validate() const { }
	#endif

protected:
	AsciiStringData* m_data;   // pointer to ref counted string data

gdb

Breakpoint 1, AsciiString::ensureUniqueBufferOfSize (this=0x7fffffffd080, numCharsNeeded=5, preserveData=false, strToCopy=0x555555dc6691 "None", strToCat=0x0) at /data/scratch/CnC/Generals/Code/GameEngine/Source/Common/System/AsciiString.cpp:126
126		validate();
(gdb) n
128		if (m_data &&
(gdb) 
140		int minBytes = sizeof(AsciiStringData) + numCharsNeeded*sizeof(char);
(gdb) p minBytes
$1 = 0
(gdb) n
141		if (minBytes > MAX_LEN)
(gdb) p minBytes
$2 = 21
(gdb) n
144		int actualBytes = TheDynamicMemoryAllocator->getActualAllocationSize(minBytes);
(gdb) 
145		AsciiStringData* newData = (AsciiStringData*)TheDynamicMemoryAllocator->allocateBytesDoNotZero(actualBytes, "STR_AsciiString::ensureUniqueBufferOfSize");
(gdb) p actualBytes
$3 = 32
(gdb) n
146		newData->m_refCount = 1;
(gdb) p newData
$4 = (AsciiString::AsciiStringData *) 0x7ffff6e92370
(gdb) n
147		newData->m_numCharsAllocated = (actualBytes - sizeof(AsciiStringData))/sizeof(char);
(gdb) p newData
$5 = (AsciiString::AsciiStringData *) 0x7ffff6e92370
(gdb) p *newData
$6 = {m_debugptr = 0x0, m_refCount = 1, m_numCharsAllocated = 0}
(gdb) n
149		newData->m_debugptr = newData->peek();	// just makes it easier to read in the debugger
(gdb) p *newData
$7 = {m_debugptr = 0x0, m_refCount = 1, m_numCharsAllocated = 16}
(gdb) n
152		if (m_data && preserveData)
(gdb) p *newData
$8 = {m_debugptr = 0x7ffff6e92374 "\377\177", m_refCount = 1, m_numCharsAllocated = 16}
(gdb) n
155			newData->peek()[0] = 0;
(gdb) p *newData
$9 = {m_debugptr = 0x7ffff6e92374 "\377\177", m_refCount = 1, m_numCharsAllocated = 16}
(gdb) n
159		if (strToCopy)
(gdb) p *newData
$10 = {m_debugptr = 0x7f00f6e92374 <error: Cannot access memory at address 0x7f00f6e92374>, m_refCount = 1, m_numCharsAllocated = 16}
(gdb) p newData
$11 = (AsciiString::AsciiStringData *) 0x7ffff6e92370
(gdb) p newData->peek()
$12 = 0x7ffff6e92374 ""

m_debugptr is initially 0x7ffff6e92374 and then suddenly becomes 0x7f00f6e92374 after newData->peek()[0] = 0;.