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Strings. Jarret Raim 2002. C Strings. Same as arrays of characters. Use pointers. Require static declarations (compile time). No bounds checking. No easy way to increase / decrease sizes. Every string must have a delimeter on the end (‘’).
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Strings Jarret Raim 2002
C Strings • Same as arrays of characters. • Use pointers. • Require static declarations (compile time). • No bounds checking. • No easy way to increase / decrease sizes. • Every string must have a delimeter on the end (‘\0’). • Must use inefficient functions from C libraries to act on the strings. • Very bad errors.
Examples • Static Declaration • char myString[20]; • Only possible to hold 19 characters, not 20. • Can’t be enlarged or shrunk. • Dynamic Declaration • char *myString = new char[ 20 ]; • Still only holds 19 characters! • Can’t easily be enlarged or shrunk.
Standard Template Library • Developed by SGI. • Contains many improved data structures. • vectors, strings, ropes, lists, deques, etc. • Comes included with most (all?) C++ distributions. • Easier to use • More portable • Faster • More functionality • Analogous to the Java String class
STL: String example string myString; myString = “Hello World!”; cout << myString << endl;
Comparison: String Concatenation char myString[10]; char anotherString[10]; char newString[20]; myString = “foo”; anotherString = “barstool”; newString = Strcat( myString, anotherString ); returns -> “foobarstool” ? Nope, crashes because myString isn’t big enough to hold “foo” + “barstool”.
Comparison: String Concatenation string myString = “times”; string anotherString = “meacupla”; string newString = “”; newString = myString + anotherString; cout << newString << endl; returns -> “timesmeaculpa”
Comparison: Substrings char c[10] = “this is a “; char subStr[3]; for( int i = 0; i < 2; i++ ) subStr[i] = c[i+1]; cout << subStr << endl; Returns -> ‘hi’
Comparison: Substrings string myString = “this is a time for all good”; string temp; temp = myString.substr( 1, 4 ); cout << temp << endl; returns -> ‘his ‘
Comparison: Comparison char temp[10] = “this is”; char t1[10] = “not equal”; if( temp[10] == t1[10] ) cout << “They are the same!” << endl; else cout << “Nope, not the same!” << endl; Returns -> “Nope, not the same!” WRONG!
Comparison: Comparison string myString = “now is the”; string newString = “time”; if( myString == newString ) cout << “They are the same!” << endl; else cout << “Nope, not the same!” << endl; Returns -> “Nope, not the same!”
Note • Most of the functionality in the STL has been written for C strings. • They are usually very hard to understand: void *memmove(void *s1, const void *s2, size_t n);void *memset(void *s, int c, size_t n);char *strcat(char *s1, const char *s2);char *strchr(const char *s, int c); [not in C++]const char *strchr(const char *s, int c); [C++ only]char *strchr(char *s, int c); [C++ only]int strcmp(const char *s1, const char *s2);
Rules for using stl::strings • No need to grow or shrink a string, just use assignment (=). • Lots of pre-made functions • Searching, sorting, substrings, copying, etc. • Easy to get the size of the string • Easy to insert and delete parts of the string • http://www.sgi.com/tech/stl/basic_string.html
Conclusions • Use STL data structures as much as you can. • You still have to understand the hard way to understand and use older code. • Look at this website to get the code for the STL and all the documentation. • http://www.sgi.com/tech/stl/
