textfiles c

8/8/2019 Textfiles C

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Programming in C:

Structures, Textfiles

Clyde Meli 2007-2008


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Overview

Structures

Files and Streams

Text File Example File Modes

Type File Example

Append File Example

Reading File Example


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Structures

Structures, unlike arrays, may contain variables of

many different data types

They are commonly used to define records to be

stored in binary files (not text files)

They can be used with pointers to build morecomplex data structures such as linked lists,

queues, stacks and trees

Example definition:

struct person {int id_no;

int alive; //0=dead,1=alive

int age;

}


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Structures (2)

struct employee {

char name[25];char surname[30];

int age;

char gender;// m or f

double monthlysalary;};

Structs cannot be compared using == and !=

You can initialise them as we did with arrays:

struct employee e1={Luke,Smith,20,m,950};

We can use the dot operator to access a struct

member eg. e1.name returns Luke.

printf(%s,e1.name)


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Structures (3)

Structures may be passed to functions by passing

individual struct members, by passing an entirestruct or by passing a pointer to a struct.

When passing a struct or individual member, it is

passed by value

The keyword typedefcan create a synonym or

alias for a previously defined data type eg

typedef struct employee Employee;

defines the new type name Employee as a

synonym for type struct employee. It could be

combined as follows

typedef struct {

.... // members

} Employee;


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Files and Streams

In C, every file is a sequential stream of bytes

Every file ends either with an EOF marker or at a

specific position in a system-maintained file

structure

When a file is opened, a stream is associated withthe file

Three files and their associated streams are opened

when program execution starts: Standard Input

(stdin), Standard Output (stdout) and StandardError (stderr)

Using function fgetc, like getchar, we can read one

character from a file. Fputc writes one character to

a file, like putchar.


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Files and Streams (2)

fputc(a,stdout) writes a to stdout, same as

putchar(a);

fgetc(stdin) gets a char from stdin, same as

getchar();

fgets and fputs can be used to read and write to afile respectively (counterparts to gets & puts)

fscanf and fprintf are the file counterparts to scanf

and printf (you can print anything to a file)

fopen is used to open a file (it has to be opened soyou can use it) and fclose is used to close it


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Files and Streams (3) - C++

ofstream is used to output to a text file

Then open(filename), close() to open & close resp.

ifstream, fstream to read, read&write resp.

Example:

#include #include using namespace std;

int main () {

ofstream myfile;myfile.open ("example.txt");myfile


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Text File Example

1

2

3

45

6

..10

// create a text file with 1..10 on every line#include

const int MAX=10;

int main(void){FILE *f;int i;f=fopen(numbers.txt,w);if (!f) return 1;//same as if (f==0)

for (i=1;i


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File Modes

fopen takes 2 arguments: a filename and a file mode.

The file mode w specifies that the file is to be written

to (and any existing file is overwritten). r means

reading, a means appending (continue writing at the

current end of the file)


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Type File Example

This example imitates the classic type command

(Win) or cat command (Unix)

#include

int main(void){FILE *f;char s[1000];

f=fopen(infile.txt,r);if (!f) return 1;while (fgets(s,1000,f)!=NULL)printf(%s,s);

fclose(f);

return 0;}


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Type File Example (C++)

This example imitates the classic type command

(Win) or cat command (Unix)

#include #include #include using namespace std;

int main(void){ifstream file;string s;file.open("infile.txt");while (!file.eof()) {

file >> s;cout


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Append File Example

11

12

13

1415

16

..20

// appends 11..20 to existing text file#include

const int MAX=20;

int main(void){FILE *f;int i;f=fopen(numbers.txt,a);if (!f) return 1;//same as if (f==0)

for (i=11;i


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Append File Example (C++)

11

12

13

1415

16

..20


// appends 11..20 to existing text file

const int MAX=20;

int main(void){ofstream file;file.open("numbers.txt",ios::app);if (file.fail()) return 1;//file does not exist, error!//note, file will ALWAYS EXIST when

appending!!!

for (int i=11;i


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Reading File Example

11

12

13

1415

16

..20

// reading integers from an existing text file#include

int main(void){

FILE *f;char s[1000];int i;f=fopen(numbers.txt,r);if (!f) return 1;//same as if (f==0)

while (fgets(s,1000,f)!=NULL) {i=atoi(s);printf(%d,i);

}fclose(f);return 0;

}


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Reading File Example (2)

atoi() does not detect errors (or arithmetic

overflows) so there is no validation on the filedata..

Something like 643abc will be converted to 643 by

atoi(), xyzabc will be coverted to 0

Using strtol to parse a number:

(char *endptr; has to be defined first)

i=strtol(s,&endptr,10);

it returns the converted value (0 if no conversion

was done, LONG_MAX or LONG_MIN if there wasan overflow). Leading whitespace in the string is

ignored


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Reading File Example - C++

11

12

13

1415

16

..20

strtol/atoi are not needed. Still should validate

inputs!


int main(void){ifstream file;int i;file.open("numbers.txt");if (file.fail()) return 1;//file does not exist, error!while (!file.eof()) {

file >> i;cout


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The End?

C++ to C#http://msdn.microsoft.com/en-us/magazine/cc301520.aspx

Java for C Programmers

http://www.d.umn.edu/~gshute/java/c2java.html

Java interface for your C program

ww.math.ucla.edu/~anderson/JAVAclass/JavaInterface/JavaInterface.html

C++ Language tutorial

http://www.cplusplus.com/doc/tutorial/
http://msdn.microsoft.com/en-us/magazine/cc301520.aspxhttp://www.math.ucla.edu/~anderson/JAVAclass/JavaInterface/JavaInterface.htmlhttp://www.cplusplus.com/doc/tutorial/http://www.cplusplus.com/doc/tutorial/http://www.math.ucla.edu/~anderson/JAVAclass/JavaInterface/JavaInterface.htmlhttp://www.d.umn.edu/~gshute/java/c2java.htmlhttp://msdn.microsoft.com/en-us/magazine/cc301520.aspx

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