Bài giảng Introduction to computer programming - Chapter 9: File Processing
Ho Chi Minh City University of Technology
Faculty of Computer Science and Engineering
Chapter 9: File Processing
Introduction to Computer Programming
(C language)
TS. Võ Thị Ngọc Châu
2017 – 2018, Semester 2
Course Content
C.1. Introduction to Computers and
Programming
C.2. C Program Structure and its
Components
C.3. Variables and Basic Data Types
C.4. Selection Statements
C.5. Repetition Statements
C.6. Functions
C.7. Arrays
C.8. Pointers
C.9. File Processing
2
References
[1] “C: How to Program”, 7th Ed. – Paul
Deitel and Harvey Deitel, Prentice Hall, 2012.
[2] “The C Programming Language”, 2nd Ed.
– Brian W. Kernighan and Dennis M. Ritchie,
Prentice Hall, 1988
and others, especially those on the Internet
3
Content
Introduction
Declare files
Open and close files
Store and retrieve data from files
Use macros
Summary
4
Recall – Chapter 3 and Chapter 8
Memory layout of a C program
Higher address
Command-line arguments
and environment variables
Local variables, arguments,
grown/shrunk with function calls
Stack
Grown/shrunk with dynamic
allocation and de-allocation
Heap
Uninitialized (static) global
variables, static local variables
Uninitialized data
Initialized to
zero by exec
.bss
Initialized (static) global variables,
static local variables, constants
Initialized data
Read from
program file
by exec
.data
Code
.text
Machine code, often read-only
Lower address
bss = block started by symbol, better save space
Introduction
Data (input, output, supporting) in memory
Temporary as lost when a program terminates !!!
Can we have permanent data before and
after program execution?
Files on secondary storage devices (hard
drives, CDs, DVDs, flash drives, …)
6
Introduction
Files on hard drives
data1.txt
data2.txt
…
7
Introduction
Figure 11.1. Data hierarchy
[1], pp. 419
8
Introduction
C views each file as a sequential stream of bytes.
Each file ends either with an end-of-file marker or at
a specific byte number recorded in a system-
maintained, administrative data structure.
end-of-file: ctrl-z (Windows), ctrl-d (Linux/Mac OS X/Unix)
When a file is opened, a stream is associated with the
file.
Streams provide communication channels between
files and programs.
Figure 11.2. C’s view of a file of n bytes
[1], pp. 420
9
Introduction
C views each file as a sequential stream of
bytes.
Fixed-length records stored in a random-access file
The exact location of a record relative to the
beginning of the file
Figure 11.10: C’s view of a random-access file
[1], pp. 431
10
Introduction
Operations on files
Create
Open
Read
Write (write a new file, append an existing file)
Close
Access to files in C for processing
Sequential access to a sequential stream of bytes
Random access to a stream of fixed-size records
11
Introduction
The standard library: <stdio.h>
FILE *fopen(const char *filename, const char *mode)
FILE *freopen(const char *filename, const char *mode,
FILE *stream)
int fclose(FILE *stream)
size_t fread(void *ptr, size_t size, size_t nmemb, FILE
*stream)
int fgetc(FILE *stream)
char *fgets(char *str, int n, FILE *stream)
int fscanf(FILE *stream, const char *format, ...)
size_t fwrite(const void *ptr, size_t size, size_t nmemb,
FILE *stream)
int fputc(int char, FILE *stream)
int fputs(const char *str, FILE *stream)
int fprintf(FILE *stream, const char *format, ...)
12
Declare files
Each file communicated with C program via a
stream controlled by a pointer of FILE
identifier: a valid identifier for a pointer
pointing to a file stream
FILE* identifier;
FILE: an object type suitable for storing
information for a file stream, defined in
the <stdio.h> standard library
FILE* pFile1;
FILE* pFile2 = 0;
FILE* pFile3 = NULL;
FILE*: a pointer type of FILE type
A file pointer will be associated with a file
stream once a file is opened.
13
Open and close files
Open files
FILE *fopen(const char *filename, const char
*mode)
Opens the file pointed to by filename using the given
opening mode.
pFile1 = fopen("Data.txt", "r");
Close files
int fclose(FILE *stream)
Closes the stream. All buffers are flushed.
fclose(pFile1);
14
Open and close files
Open files
Filename = "Data.txt"
Located in the current directory
Filename = ".\\Data\\Data.txt"
Located in the sub-directory of the current directory
Filename = "..\\Data.txt"
Located in the super-directory of the current directory
Filename = "D:\\CS - Introduction to Computer
Programming - CO1003 - Undergraduate
course\\Code samples\\Data\\Data.txt"
Located in the specified directory with the absolute path
15
…
Open and close files
File opening modes
16
Store and retrieve data from files
Store data into files (write)
A sequence of bytes from memory to the file
The file plays a role of stdout.
Retrieve data from files (read)
A sequence of bytes from the files to memory
The file plays a role of stdin.
What bytes?
A char
Read (file -> memory)
Write (memory -> file)
fgetc
fgets
fputc
fputs
fprintf
fwrite
A line of bytes
Formatted bytes fscanf
Bytes in the
binary mode
fread
Store and retrieve data from files
Store and retrieve data from files
Store and retrieve data from files
What bytes?
Read (file -> memory)
Write (memory -> file)
A char
fgetc
fputc
char aChar;
A line of bytes
char aStr[50];
aChar = fgetc(pFile1);
fgets
fputc('a', pFile1);
fputs
fgets(aStr, 50, pFile1);
fputs("Today?", pFile1);
fprintf
Formatted bytes fscanf
int anInt;
char aChar;
float aFloat;
fscanf(pFile1, "%d %c
%f", &anInt, &aChar,
&aFloat);
fprintf(pFile1, "%d %d
%c %f", 10, anInt, aChar,
aFloat);
Bytes in the
binary mode
fread
fwrite
char buffer[50]; fread(buffer,
fwrite(buffer,
sizeof(int)+sizeof(char)+si strlen(buffer)+1, 1,
zeof(float)+1, 5, pFile1); pFile1);
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