Chapter Nine Strings

Char vs String Literals Size of data types: Size of data types: –sizeof(“hello\n”)7 bytes –sizeof(“hello”)6 bytes –sizeof(“X”)2 bytes –sizeof(‘x’)1 byte Every string in C++ is an array of characters with a NULL terminator to mark the end Every string in C++ is an array of characters with a NULL terminator to mark the end An array of characters w/o a NULL is not a string An array of characters w/o a NULL is not a string

char st3[5] will not compile: “initializer-string for array of chars is too long” - no room for \0

String I/O Functions All library functions assume your array of characters includes a NULL terminator. If not, result may be “segmentation fault, core dumped” iostream.h iostream.h coutprints all characters up to \0 cinreads a word (stops at a space) into a char array, appends a \0 cin.getlinereads a complete line of input into a char array, appends a \0 cin.getreads a single character, no \0

getline() Symtax getline, one of cin’s functions, uses default arguments for the length of the line to read, and the character to stop on. void cin.getline(char str[], int = 80, char = ‘\n’); dot cin’s getline function dot cin’s getline function cin.getline(name,80,’\n’);read at most 80 chars stop on newline cin.getline(name, 40, ‘\t’);read at most 40 chars stop on tab

Size matters If maximum length of first name is 20 char first[21]; If maximum length of last name is 30 char last[31]; If there will be at most two spaces between first and last names: char name[53];// \0 Invalid size character array declaration is a common cause of errors and system vulnerabilities

Reminder Strings are arrays of characters with a NULL marker or sentinel at the end Strings are arrays of characters with a NULL marker or sentinel at the end Array names are constant pointers to the element type Array names are constant pointers to the element type Other pointers can be used to access elements (offset or indices) Other pointers can be used to access elements (offset or indices) NULL is defined to be 0 (false) NULL is defined to be 0 (false)

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Slide 5 of 32 This final version is very similar to the strcpy() included in the C++ string library

Visiting the Library C++ has an extensive library of string- handling functions C++ has an extensive library of string- handling functions Every C++ string function expects a pointer to an array of characters terminated by a NULL character Every C++ string function expects a pointer to an array of characters terminated by a NULL character Unterminated strings are a common cause of segmentation faults Unterminated strings are a common cause of segmentation faults Failure to check bounds is a common cause of system vulnerabilities Failure to check bounds is a common cause of system vulnerabilities

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Slide 18 of 32 Note how much more memory is required by c4 – 80 bytes vs 16 bytes for c bytes for the strings stored “somewhere”

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Errors char msg[5] = “Error”; // not enough space char line[80];// for 80 char line, need 81 in array Forgetting to put NULL into string Reading beyond end of array. Often happens because library routine expects to find a NULL Buffer overflow. Writing beyond end of array char *newloc; strcpy(newloc,“Don’t try this”); // need char* but must also have a block of memory set aside