String Class
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s1 |
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Class String { private: char* m_szData; unsigned m_nlength; //object variable static unsigned s_nCount; //class variable public: String(); String(char*, szString); } |
cs |
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ds |
data |
lenth |
count |
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stack |
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heap |
"This is not a test" |
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(s1 pointer for ds: __,data,length) |
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int main() P String S1("This is not a test!); |
Static member variable, refers to the class and not the object or any object, not part of any object. Exists for entire execution of program regardless of whether there is a string or not...access through a string object.
Global Variables. Constants. Variables declare as static. (Global variable: accessable at anytime from anywhere.) |
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int Factorial(int nIndex) { static int s=0; if(nIndex ==1) { return1; } else { return nIndex * Fact(nIndex –1); } s++; } --stored in DS not heap --if wasn’t static, would be stored in heap |
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#2
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Class String { private: char* m_szData; unsigned m_nlength; //object variable static unsigned s_nCount; //class variable public: String(); String(char*, szString); } |
//String.cpp unsigned string::s_nCount = 0; String::String() { m_nlength = 0; n_szData = NULL; s_nCount++; } String::String(char* szString) //how many string objects are being created { m_nLength = strlen(szString); m_szData = new char[m_nLength+1]; strcpy(n_szData, szString); s_nCount++; } |
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Class String { private: char* m_szData; unsigned m_nlength; //object variable static unsigned s_nCount; //class variable public: String(); String(char*, szString); private: static void IncCount(); } |
//String.cpp unsigned string::s_nCount = 0; String::String() { m_nlength = 0; n_szData = NULL; IncCount(); } String::String(char* szString) //how many string objects are being created { m_nLength = strlen(szString); m_szData = new char[m_nLength+1]; strcpy(n_szData, szString); IncCount(); } |
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A static method cannot directly access an object variable //but can reference (pointers) void string::IncCount() { s_nCount++; m_nLength =0; //not legal if IncCount is static, is legal if IncCount is not static }
//static method: void BankAccount::Get NextAfccountNumber(char* szNum) //pointer accesses the variable //void BankAccount::Get NextAfccountNumber(char* szAcct) { |
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#3
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Class String { private: char* m_szData; unsigned m_nlength; //object variable static unsigned s_nCount; //class variable public: String(); String(char*, szString); private: static void IncCount(); public: string operator + (char* szString); } |
string s1 ("This is a"); string s2 = s1 + "test!"; //s2 -> "’this is a test!"
String String::operator + (char* szStr) { int nSize = n_nLength + strlen(szStr); char* ptemp = new char [nSize +1] ; if (n_szData !=NUll) { strcpy (ptemp, n_szData); } if(szStr !=Null) { strcpy(ptemp + m_nlength, sz Str); } //character array that is a concatenation of two strings string ret(ptemp); return ret; } |
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Class String { private: char* m_szData; unsigned m_nlength; //object variable static unsigned s_nCount; //class variable public: String(); String(char*, szString); private: static void IncCount(); public: string operator + (char* szString); string operator + (char& s); } |
string s1 ("This is a"); string s2 = s1 + "test!"; //s2 -> "’this is a test!" string s3 = s2 +s1; String String::operator + (char* szStr) { int nSize = n_nLength + strlen(szStr); char* ptemp = new char [nSize +1] ; if (n_szData !=NULL { strcpy (ptemp, n_szData); } if(szStr !=Null) { strcpy (ptemp + m_nlength, sz Str); } //character array that is a concatenation of two strings string ret(ptemp); delete [ ] pTemp; return ret; } string string:: operator +(Stirng & s) { int nSize = n_nLength + s. m_nLength; char* pTemp = now char [nSize +1]; if (m_nLength !=0) { strcpy(pTemp, m_szData); { if(s.n_nLength !=) { strcpy(ptemp + n_nLength, s. n_szData); } String ret(pTemp); delete[ ]pTemp; return ret, } |
