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Chapter Nine. Strings. Char vs String Literals. 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 - PowerPoint PPT Presentation
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Chapter NineChapter Nine
StringsStrings
Char vs String LiteralsChar vs String Literals Size of data types:Size of data types:
– sizeof(“hello\n”)sizeof(“hello\n”) 7 bytes7 bytes– sizeof(“hello”)sizeof(“hello”) 6 bytes 6 bytes – sizeof(“X”)sizeof(“X”) 2 bytes2 bytes– sizeof(‘x’)sizeof(‘x’) 1 byte1 byte
Every string in C++ is an array of characters Every string in C++ is an array of characters with a NULL terminator to mark the endwith a NULL terminator to mark the end
An array of characters w/o a NULL is not a An array of characters w/o a NULL is not a stringstring
char st3[5] will not compile: “initializer-string for array of chars is too long” - no room for \0
String I/O FunctionsString I/O Functions
All library functions assume your array of characters All library functions assume your array of characters includes a NULL terminator. If not, result may be includes a NULL terminator. If not, result may be “segmentation fault, core dumped”“segmentation fault, core dumped”
iostream.hiostream.hcoutcout prints all characters up to prints all characters up to \\00cincin reads a word (stops at a space) into a reads a word (stops at a space) into a
char array, appends a char array, appends a \\00cin.getlinecin.getline reads a complete line of input into a reads a complete line of input into a
char array, appends a char array, appends a \\00cin.getcin.get reads a single character, no reads a single character, no \\00
getline()getline() Symtax Symtax
getlinegetline, one of cin’s functions, uses default arguments , one of cin’s functions, uses default arguments for the length of the line to read, and the character to for the length of the line to read, and the character to stop on.stop on.
void void cin.getlinecin.getline(char str[], int = 80, char = ‘\n’);(char str[], int = 80, char = ‘\n’); dot cin’s getline functiondot cin’s getline function
cin.getline(name,80,’\n’);cin.getline(name,80,’\n’); read at most 80 chars read at most 80 chars stop on newlinestop on newline
cin.getline(name, 40, ‘\t’);cin.getline(name, 40, ‘\t’); read at most 40 chars read at most 40 chars stop on tabstop on tab
Size mattersSize matters
If maximum length of first name is 20If maximum length of first name is 20
char first[21];char first[21];
If maximum length of last name is 30If maximum length of last name is 30
char last[31];char last[31];
If there will be at most two spaces between first and last If there will be at most two spaces between first and last names:names:
char name[53];char name[53]; // 20 + 2 + 30 + \0// 20 + 2 + 30 + \0
Invalid size character array declaration is a common Invalid size character array declaration is a common cause of errors and system vulnerabilitiescause of errors and system vulnerabilities
ReminderReminder
Strings are arrays of characters with Strings are arrays of characters with a NULL marker or sentinel at the enda NULL marker or sentinel at the end
Array names are constant pointers to Array names are constant pointers to the element typethe element type
Other pointers can be used to access Other pointers can be used to access elements (offset or indices)elements (offset or indices)
NULL is defined to be 0 (false)NULL is defined to be 0 (false)
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// When loop finished, append NULL
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This final version is very similar to the strcpy() included in the C++ string library
Visiting the LibraryVisiting the Library
C++ has an extensive library of C++ has an extensive library of string-handling functionsstring-handling functions
Every C++ string function expects a Every C++ string function expects a pointer to an array of characters pointer to an array of characters terminated by a NULL characterterminated by a NULL character
Unterminated strings are a common Unterminated strings are a common cause of segmentation faultscause of segmentation faults
Failure to check bounds is a common Failure to check bounds is a common cause of system vulnerabilitiescause 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 c5 + 15 bytes for the strings stored “somewhere”
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ErrorsErrors
char msg[5] = “Error”; // not enough spacechar msg[5] = “Error”; // not enough space
char line[80];char line[80]; // for 80 char line, need 81 in // for 80 char line, need 81 in arrayarray
Forgetting to put NULL into stringForgetting to put NULL into string
Reading beyond end of array. Often happens Reading beyond end of array. Often happens because library routine expects to find a NULLbecause library routine expects to find a NULL
Buffer overflow. Writing beyond end of arrayBuffer overflow. Writing beyond end of array
char *newloc;char *newloc;
strcpy(newloc,“Don’t try this”);strcpy(newloc,“Don’t try this”);
// need char* but must also have a block of // need char* but must also have a block of memory set asidememory set aside
