Lecture 3 - File I/O Flashcards
1
Q
include
A
- always pulls a header file into another file
- ex. #include “file.h” pull in file.h from present directory
- ex. #include <file.h></file.h>
- pulls the file from /user/include/file.h
2
Q
boolean variables
A
- we can use variables of type “bool” and assign values of true or false to them
- you need to #include <stdbool.h> to do this</stdbool.h>
3
Q
fopen()
A
- FILE *fopen(char *file_name, char *mode);
- file_name: name of file
- mode: will we read it, write it, or both?
4
Q
modes for fopen()
A
- “r”: opens the file only for reading, must already exist
- “w”: creates a file for writing or overwrites the given file
- “a”: appends to the end of a file if it exists or creates and writes to it
5
Q
fopen() return values
A
- if successful, fopen() opens the file and returns a FILE pointer to represent the file
- if not successful, returns a NULL pointer
- doesn’t matter what file points to as long as it’s not NULL
- ALWAYS CHECK THE RETURN VALUE
6
Q
fclose()
A
- int close(FILE *file_pointer);
- every successfully opened file must be closed when we are finished with it
- when the file is closed its internal data is flushed
- does NOT set the file pointer to null
- you should manually set it AFTER fclose()
7
Q
fclose() return values
A
- on success, fclose() returns a 0
- on failure, fclose() returns EOF
8
Q
fprintf()
A
- fprintf(FILE *stream, const char *format, …)
- works just like printf() except it takes an extra FILE pointer argument (writes to file)
- printf(“Hello, world”); is equivalent to fprintf(stdout, “Hello, world”);
9
Q
reading data in c
A
- c is a little different than Java when it comes to reading data
- think printf() in reverse
ex. scan(“%d %d”, buffer, &int_var); - returns number of successful data conversions
10
Q
fscanf()
A
- works just like scans() except that it takes an extra FILE pointer argument (reads file)
- the following are equivalent.. scans(“%s”, buffer);
fscanf(stdin, “%s”, buffer);
11
Q
proper error checking with a file
A
-check that the file isn’t NULL after trying to open it
- fclose() the file after you’re done
- set the file to NULL after closing it
12
Q
file I/O essentials
A
- in a program we refer to files with FILE pointers
- a file must be OPENED before writing or reading from it (except stdin, stdout, stderr)
13
Q
feof()
A
- int feof (FILE *ptr)
- checks to
- used to check to see if try to read past file end
- returns 0 if the end of file has not been reached and nonzero if it has
14
Q
ferror()
A
- int ferror(FILE *ptr)
- used to check if a file stream encountered an error during reading or writing
- returns 0 if no error occurred and nonzero if one did
- does not stop execution when an error occurs, just sets an internal error flag for the file
15
Q
clearerr()
A
- void clearerr(FILE *ptr)
- used to reset the error and end of file flags for a file stream if they exists
- files set flags internally to mark errors/EOF, clearerr removes them so file can operate w/o issues
16
Q
fwrite()
A
- size_t fwrite(const void *ptr, size_t size, size_t count, FILE *stream);
- ptr is data to be written, size is size of each element, count is number of elements to write, stream is file pointer to write to
- used to write binary data to a file
- returns the number of elements to be written (less if error occurred)
17
Q
fread()
A
- size_t fread(void *ptr, size_t size, size_t count, FILE *stream)
- prt is pointer to memory where the data will be stored
- size is size in bytes of each element
- count is number of elements to read
- steam is file pointer
- returns number of elements successfully read (less than if error)
18
Q
stdout
A
- the default output stream in C (short for standard output)
- directs output to the console/terminal
- used by printf(), fprintf() and puts()
- ex. fprintf(stdout, “Hi!”);
19
Q
printf()
A
- used to print formatted text to stdout
- int printf(const char *format, …);
- format specifies how the text should be printed
- … allows passing multiple arguments to be formatted
- returns number of characters printed
