Fundamental File Processing Operations C++

C++ Standard Input and Output The stream model of text input/output. A text stream consists of a sequence of lines; A line consists of zero or more characters terminated with a newline ('\n') character. Even if the computer system does not conform to that model, the library must hide the deviations

C++ Standard Input and Output C++ has three pre-opened streams as well: cin standard input connected to keyboard cout standard output connected to screen cerr standard output for error messages to screen

File Access Introduction Writing cout (stdout) and reading from cin (stdin is) very similar to file I/O; C++ (C) treats cin (stdin) and cout (stdout) as files. The major difference is that cxxx (stdxxx) are already connected to the program (and opened) by the system

Input/Output Redirection On MS-DOS and UNIX systems, prog > outfile.dat redirects all cin (stdout) output to 'outfile.dat'. Likewise, input redirection prog1 < infile.dat reads from 'infile.dat', for every cin (stdin) input.

Input/Output Redirection prog2 < infile.dat > outfile.dat reads from ‘infile.dat’ and outputs to 'outfile.dat'.

File creation/replacement In the previous examples: if 'outfile.dat' exists, it is deleted and replaced, if it does not exist, it is created.

File Appending If you want to APPEND to the current 'outfile.dat', use prog >> outfile.dat (>> means append).

C++ header files C stdio.h - types and operations used for C streams C++ iostream.h - stream operations fstream.h - file stream operations

C++ Stream classes C++ streams are implemented as classes ostream - output stream istream - input stream cin, cout, and cerr are three predefined instances of streams cin - is an instance of istream cout and cerr are instances of ostream These streams are defined in iostream.h File manipulation methods are defined in fstream.h

C++ Stream constructors fstream (); leave the stream unopened fstream (char * filename, int mode); open the file filename using mode mode Mode integer defined as ios enumerators: ios::in - open for input ios:out - open for output ios:trunc - (for output) discard contents ios:app - (for output) append to the end of file ios:nocreate - causes open to fail if file does not exist ios:binary - opens in binary mode (text is default)

C++ Stream destructors ~fstream(); destroys the fstream object. File is closed of openned by the constructor or the open member function.

C++ Stream Methods int open(char * filename, int mode); int read(unsigned char * dest_addr, int size); int write(unsigned char * source addr, int size) Read and write allow for unformatted (raw) I/O

C++ Formatted Stream I/O operators << output to fstream defined for all built in data types >> input from fstream Also defined for all built in data types It is important to understand that these operators format based on the passes datatype Many modi

fstream subclasses ifstream ofstream for input ios:in implied ofstream for output ios:out implied All the fstream methods are inherited.

Example: C++ File listing program #include <fstream.h> void main () { char ch; fstream file; // declare fstream unattached char filename[20]; cout <<"Enter the name of the file: " <<flush; // force output cin >> filename; file.open(filename, ios::in); file.unsetf(ios::skipws); // include white space in read while (1) { file >> ch; if (file.fail()) break; cout << ch; } file.close(); }

fstream Format manipulators Stream I/O can be modified with the format manipulators setf and unsetf. These functions set and clear bits in the format flags. ios::setf(long iFlags); ios::unsetf(lond iFlags); Flags may be “or”ed together with the “|” operator Example: myfile.setf(ios::hex | ios::left);

fstream Format Flags ios::skipws - Skip white space on input. ios::left - Left align values; pad on the right with the fill character. ios::right - Right align values; pad on the left with the fill character (default alignment). ios::internal - Add fill characters after any leading sign or base indication, but before the value. ios::dec - Format numeric values as base 10 (decimal) (default radix). ios::oct - Format numeric values as base 8 (octal). ios::hex - Format numeric values as base 16 (hexadecimal).

fstream Format Flags ios::showbase - Display numeric constants in a format that can be read by the C++ compiler. ios::showpoint - Show decimal point and trailing zeros for floating-point values. ios::uppercase - Display uppercase A through F for hexadecimal values and E for scientific values. ios::showpos - Show plus signs (+) for positive values. ios::scientific - Display floating-point numbers in scientific format. ios::fixed - Display floating-point numbers in fixed format. ios::unitbuf - Cause ostream::osfx to flush the stream after each insertion. By default, cerr is unit buffered. ios::stdio - Cause ostream::osfx to flush stdout and stderr after each insertion.

Seeking with C++ stream classes Two forms: file.seekg(long position); file.seekg(long offset, origin); position - position in file offset - byte offset from origin origin ios::beg ios:::cur ios::end

C Command Line Parameters Two values passed to main: int argc - Number of command line arguments (including command) char *argv[] - Array of pointers to parameter strings. argc >=1 *argv[0] is always a string containing the file name *argv[1] is the first argument, and so on

String Handling string.h definitions char *strcat (char *dest, const char *src); concatenate src to end of dest.

String Handling char *strncat(char *dest, const char *src, size_t maxlen); concatenate maxlen chars of src onto dest.

String Handling char * strchr(const char *s, int c); return pointer to first c in s, NULL if not present. char *strrchr(const char *s, return pointer to last c in s, NULL if not present.

String Handling int strcmp(const char *s1, const char *s2); return negative if s1 lexically less than s2 return 0 if s1==s2; return positive if s1>s2.

String Handling int strncmp(const char *s1, const char *s2, size_t maxlen); same as strcmp, but only uses n chars.

String Handling char *strcpy (char *dest, const char *src); copy src to dest. char *strncpy(char *dest, const char *src, size_t maxlen); same as strcpy, only n chars.

String Handling size_t strlen (const char *s); returns length of s;

Strings example main() { char name1[12],name2[12],mixed[25]; char title[20]; strcpy(name1,"Rosalinda"); strcpy(name2,"Zeke"); strcpy(title,"This is the title."); printf(" %s\n\n",title); printf("Name 1 is %s\n",name1); printf("Name 2 is %s\n",name2); if(strcmp(name1,name2)>0) /* returns 1 if name1 > name2 */ strcpy(mixed,name1); else strcpy(mixed,name2); printf("The biggest name alpabetically is %s\n",mixed); strcat(mixed," "); strcat(mixed,name2); printf("Both names are %s\n",mixed); }