fopen(file_name, access_mode)

The file_name is the name of the file to be accessed and it may also include the path. The access_mode defines whether the file is open for reading, writing or appending data. Table 9.1 summarises the access modes supported by fopen function.

Table 9.1 – File access modes

FILE *fp;

fp = fopen("my file.txt", "a");

The function fopen returns a pointer (referred as the file pointer) to the structure⁶ FILE which is defined in the stdio.h headier file. When you open a file it would be better to make sure that the

operation is successful. If the establishment of a connection is successful the function returns a pointer to the file. If an error is encountered while establishing a connection the functions returns NULL.

9.1.2 Closing the Connection to a File

After a connection to a file is established it can be used to read or write data. When all the file processing is over the connection should be closed. Closing the connection is important as it writes any remaining data in the buffer to the output file. The function fclose is used to close the file. For example:

fclose(fp)

When closing the file the file pointer “fp” is used as an argument of the function. When a file is successfully closed the function fclose returns a zero and any other value indicates an error.

You can assign the output of the function getc to an int or char variable.

Hello World!

This is my first file

The following program reads the file “my file.txt” one character at a time and displays it on the screen.

/* Program-9 . 1 * / #include
void main() {

FILE *fp;

char c;
fp = fopen("my text.txt", "r"); //open read-only if (fp != NULL)

{

c = getc(fp); //read the 1st character

{

printf (" %c" ,c) ;

}

fclose(fp); //close the file

else

Execution of Program-9.1 will display

Hello World!

This is my first file

In Program-9.1 a connection is first established to the file. Then the expression if(fp != NULL) evaluates whether the connection is successful. If it is not successful the program will display the message “Error while opening file...” If it is successful it reads the first character from the file. If the character is not the end of the file (indicated by the End Of File (EOF) mark) it displays the

character. Then the program continues to read the rest of the characters in the file until it finds the EOF mark. Afterwards the connection to the file is closed using the fclose function.

In real-life applications it is more useful to read one string at a time rather than one character. With every read, the program has to check for the line feed (LF) character so it can find the end of each string. Also it must check for the EOF mark which comes at the end of the file . The fgets function can be used to read a string at a time. The function generally takes the form:

/* Program-9 . 3 * /

#include
void main()

{

FILE *fp;

int i; //loop counter char *message;

message = "Introduction C Programming";

fp = fopen("c:\\message.txt", "w"); //open for writing

if(fp != NULL) //if success

{

for (i =0 ; i < strlen(message);i++)

putc(*(message+i),fp); //write character pointed by pointer
fclose(fp); //close the file

} else

printf("\nError while opening file");

}

Writing a String to a File

The advantage of putc is that it allows you to control every byte that you write into the file. However sometimes you may want to write one string at a time. Two functions, namely fputs and fprintf can be used for this purpose. The fprintf function is identical to the printf function only difference being that it writes to a file rather than to the screen. The format of each function is:

fputs(string, file_pointer) fprintf(file_pointer, “%s”, string)

Exercise 9.1 – Modify Program-9.3 such that it uses the fputs rather than the fputc function to write the message to the file .

Exercise 9.2 – Develop a simple telephone directory which saves your friends contact information in a file named directory.txt. The program should have a menu similar to the following:

Menu

1. 
   Add new friend.
   
2. 
   Display contact info.
   
3. 
   Exit
   

• 
  ----------------------------------------------‑
  

Enter menu number:

When you press “1” it should request you to enter following data:

New friend info Name : Saman

Phone-No: 011-2123456

e-Mail : saman@cse.mrt.ac.lk

After adding new contact information it should again display the menu. When you press “2” it should display all the contact information stored in the directory.txt file as follows:

Contact info

Name Tel-No e-Mail

Kamala	077-7123123	kamala@yahoo.com
Kalani	033-4100101	kalani@gmail.com
Saman	011-2123456	saman@cse.mrt.ac.lk

• 
  ---------------------------‑
  

• 
  ----------‑
  

© Department of Computer Science and Engineering
Library Functions

The C language is accomplished by a number of library functions that performs various tasks. Following is a list of commonly used functions. For a more complete list reader should refer to the manual (or help) of the version of C compiler that is being used.

H.1 Character Manipulation Functions

Function	Header file	Prototype	description
isalnum	ctype.h	int isalnum(int character)	Determines if the character is alphanumeric. If true return nonzero value, else 0.
isalpha	ctype.h	int isalpha(int character)	Determines if the character is alphabetic. If true return nonzero value, else 0.
isascii	ctype.h	int isascii(int character)	Determines if the character is an ASCII character. If true return nonzero value, else 0.
isdigit	ctype.h	int isdigit(int character)	Determines if the character is a decimal digit. If true return nonzero value, else 0.
islower	ctype.h	int islower(int character)	Determines if the character is a lowercase. If true return nonzero value, else 0.
ispunct	ctype.h	int ispunct(int character)	Determines if the character is a punctuation character. If true return nonzero value, else 0.
isspace	ctype.h	int isspace(int character)	Determines if the character is a whitespace. If true return nonzero value, else 0.
isupper	ctype.h	int isupper(int character)	Determines if the character is a uppercase. If true return nonzero value, else 0.
isxdigit	ctype.h	int isdigit(int character)	Determines if the character is a hexadecimal digit. If true return nonzero value, else 0.
toascii	ctype.h	int toascii(int character)	Convert value of argument to ASCII.
tolower	ctype.h	int tolower(int character)	Convert a character to lowercase.
toupper	ctype.h	int toupper(int character)	Convert a character to uppercase.

H.2 String Manipulation Functions

Function	Header file	Prototype	description
strcmp	string.h	int strcmp(char *str1, char *str2)	Compare 2 strings. Return negative value if str1 < str2, return positive value is str1 > str2 and if both are identical
strcmpi	string.h	int strcmpi(char *str1,char *str2)	Compare 2 strings without considering the case. Return negative value if str1 < str2, return positive value is str1 > str2 and if both are identical
strcpy	string.h	char *strcpy(char *str1, char * str2)	Copy str2 to str1.
strlen	string.h	int strlen(char *str)	Count the number of characters in a string.

H.3 Mathematical Functions

Function	Header file	Prototype	description
abs	stdlib.h	int abs(int x)	Return absolute value of x.
acos	math.h	double acos(double radians)	Return the arc cosine.

Asin	math.h	double asin(double radians)	Return the arc sine.
Atan	math.h	double atan(double radians)	Return the arc tangent.
Ceil	math.h	double atan(double value)	Return a value rounded up to the next higher integer
Cos	math.h	double cos(double radians)	Return the cosine.
Exp	math.h	double exp(double x)	Raise e to the power x.
Fabs	math.h	double fabs(double x)	Return the absolute value of x.
Log	math.h	double log(double x)	Return the natural logarithm of x.
log10	math.h	double log10(double x)	Return the logarithm of x (base 10).
Pow	math.h	double pow(double x, double y)	x . Return y
Sin	math.h	double sin(double radians)	Return the sine.
Sqrt	math.h	double sqrt(double x)	Return square root of x.
Tan	math.h	double tan(double radians)	Return the tangent.

H.4 I/O Functions

Function	Header file	Prototype	Description
fclose	stdio.h	int fclose(FILE *fp)	Close file pointed by fp.
Feof	stdio.h	int feof(FILE *fp)	Determine whether end of file is reached. If so return none zero else zero is returned.
Fgetc	stdio.h	int fgetc(FILE *fp)	Read single character from file.
Fgets	stdio.h	char *fgets(char *buffer, int sizeofbuffer, FILE *fp)	Read single string from file
Fopen	stdio.h	FILE *fopen(char *filename, char *accessmode)	Open file.
fprintf	stdio.h	int fprintf(FILE *fp, char *format, arg1, arg2, …)	Send data (arg1, arg2, ..) to file of the given data format.
Fputc	stdio.h	Int fputc(char c, FILE *fp)	Send character to file.
Fputs	stdio.h	Int fputs(char *string, FILE *fp)	Send string to file.
Getc	stdio.h	int getc(FILE *fp)	Enter single character from file.
Gets	stdio.h	char *gets(char *string)	Enter string from standard input.
Puts	stdio.h	int *gets(char *string)	Send string to standard output.

H.5 Miscellaneous Functions

Function	Header file	Prototype	description
Exit	stdlib.h	void exit(int number)	Close all files and buffers and terminate the program.
Kbhit	conio.h	int kbhit(void)	Is a key press. If key is pressed return nonzero and if not

C programming R K Pandey

Directory: 2013
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