File handling functionsIn this article, we will cover the following functions that are popularly used in file handling :fopen()FILE *fopen(const char *path, const char *mode);The fopen() function is used to open a file and associates an I/O stream with it. This function takes two arguments. The first argument is a pointer to a string containing name of the file to be opened while the second argument is the mode in which the file is to be opened. The mode can be : r : Open text file for reading. The stream is positioned at the beginning of the file. r+ : Open for reading and writing. The stream is positioned at the beginning of the file. w : Truncate file to zero length or create text file for writing. The stream is positioned at the beginning of the file. w+ : Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file. a : Open for appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file. a+ : Open for reading and appending (writing at end of file). The file is created if it does not exist. The initial file position for reading is at the beginning of the file, but output is always appended to the end of the file.The fopen() function returns a FILE stream pointer on success while it returns NULL in case of a failure.fread() and fwrite()size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);

size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);The functions fread/fwrite are used for reading/writing data from/to the file opened by fopen function. These functions accept three arguments. The first argument is a pointer to buffer used for reading/writing the data. The data read/written is in the form of nmemb elements each size bytes long.In case of success, fread/fwrite return the number of bytes actually read/written from/to the stream opened by fopen function. In case of failure, a lesser number of byes (then requested to read/write) is returned.fseek()int fseek(FILE *stream, long offset, int whence);The fseek() function is used to set the file position indicator for the stream to a new position. This function accepts three arguments. The first argument is the FILE stream pointer returned by the fopen() function. The second argument offset tells the amount of bytes to seek. The third argument whence tells from where the seek of offset number of bytes is to be done. The available values for whence are SEEK_SET, SEEK_CUR, or SEEK_END. These three values (in order) depict the start of the file, the current position and the end of the file.Upon success, this function returns 0, otherwise it returns -1.fclose()int fclose(FILE *fp);The fclose() function first flushes the stream opened by fopen() and then closes the underlying descriptor. Upon successful completion this function returns 0 else end of file (eof) is returned. In case of failure, if the stream is accessed further then the behavior remains undefined.The codeThe simplest way that C programming information is stored in a file issequentially,one byte after the other. The file contains one long stream of data.File access in C is simply another form of I/O. Rather than go to the display, the input or output goes into a file. A file is opened by using the fopen() function:handle = fopen(filename,mode);The fopen() function requires two arguments, both strings. The first is afilename; the second is amode. The fopen() function returns a filehandle, which is a pointer used to reference the file. That pointer is a FILE type of variable.ModeFile Open forCreate File?Notes

"a"AppendingYesIt adds to the end of an existing file; a file is created if it doesnt exist.

" a+"Appending and readingYesInformation is added to the end of the file.

"r"ReadingNoIf the file doesnt exist, fopen() returns an error.

"r+"Reading and writingNoIf the file doesnt exist, an error is returned.

"w"WritingYesThe existing file is overwritten if the same name is used.

"w+"Writing and readingYesThe existing file is overwritten.

Themodeis a string. Even when only one character is specified, it must be enclosed in double quotes.After the file is open, you use thehandlevariable to reference the file as you read and write. The file I/O functions are similar to their standard I/O counterparts, but with an f prefix. To write to a file, you can use the fprintf(), fputs(), fputchar(), and similar functions. Reading from a file uses the fscanf(), fgets(), and similar functions.You close the file by using the fclose() function with the file handle as its argument.How to write text to a fileWrite That File demonstrates the basic process of creating a new file, writing text to that file, and then closing file access.WRITE THAT FILE#include #include int main(){ FILE *fh; fh=fopen("hello.txt","w"); if(fh==NULL) { puts("Can't open that file!"); exit(1); } fprintf(fh,"Look what I made!\n"); fclose(fh); return(0);}Line 6 creates the file handle, fh. Its a pointer. The pointer stores the result of the fopen() function from Line 8. The file hello.txt is created using the "w" (write) mode. If the file exists, its overwritten.The if statement checks to confirm that the file was properly opened. If it wasnt, the value of fh is NULL, and appropriate action is taken.The fprintf() function writes text to the file at Line 14. The format is the same as for printf(), although the file handle must be included as an argument.Finally, Line 15 closes the file by using the fclose() function. This statement is a required step for any file access programming.Exercise1:Copy the source code from Write That File into your editor. Build and run the program.The programs output goes to a file, so you dont see anything displayed when its run. Use your computers file browser to locate the file and open it. Or you can write a program that reads the text from that same file.How to read text from a fileThe standard C text-reading functions are used to read text from a file just as they read text from the keyboard. For reading text one character at a time, use the fgetc() function.READ THAT FILE#include #include int main(){ FILE *fh; int ch; fh=fopen("hello.txt","r"); if(fh==NULL) { puts("Can't open that file!"); exit(1); } while((ch=fgetc(fh))!=EOF) putchar(ch); fclose(fh); return(0);}Line 9 in Read That File opens the file hello.txt for reading only. The file must exist or else an error occurs.The while loop at Line 15 displays the files contents one character at a time. The fgetc() function reads one character from the file identified by handle fh. That character is stored in variable ch. The result is compared with the End of File constant. When theres a match, the file has been completely read and the while loop stops. Otherwise, the character thats read is displayed on Line 16.Exercise2:Create a new program by using the source code shown in Read That File. Build and run.The program displays the contents of the file created by Exercise 1; otherwise, you see the error message.Exercise3:Modify your source code from Exercise 1 to write a second string to the file. Add the following statement after Line 14:fputs("My C program wrote this file.\n",fh);Unlike using the puts() statement, you need to specify a newline character for fputs() output. Further, the file handle argument appears after the string, which is unusual for a C language file function.The two file-writing functions fprintf() and fputs() write text to the file sequentially, one character after the other. The process works just like writing text to the screen, but instead those characters are saved in a file in permanent storage.The fgets() function reads an entire string of text from a file. To make it work, you need an input buffer, the number of characters to read, and the file handle.GULPING STRINGS OF TEXT#include #include int main(){ FILE *fh; char buffer[64]; fh=fopen("hello.txt","r"); if(fh==NULL) { puts("Can't open that file!"); exit(1); } while(fgets(buffer,64,fh)) printf("%s",buffer); fclose(fh); return(0);}The fgets() function appears at Line 15 as the while loops condition. Thats because fgets() returns a pointer to the string thats read, and when no string is read, it returns a NULL. That value stops the loop. Otherwise, the printf() function at Line 16 displays the input.The buffer size and the size of characters read in Gulping Strings of Text are identical. Thats because the \0 at the end of the string is read from the file and isnt interpreted as an end-of-file marker.Exercise4:Type the source code from Gulping Strings of Text into your editor. Build and run.This lesson is about using random access files in C and the following lesson will look at working with text files. Apart from the simplest of applications, most programs have to read or write files. Maybe it's just for reading a config file, or a text parser or something more sophisticated. The basic file operations are fopen - open a file- specify how its opened (read/write) and type (binary/text) fclose - close an opened file fread - read from a file fwrite - write to a file fseek/fsetpos - move a file pointer to somewhere in a file. ftell/fgetpos - tell you where the file pointer is located.There are two fundamental types of file: text and binary. Of these two, binary are generally the simpler to deal with. As doing random access on a text file isn't something you need to do too often, we'll stick with binary files for the rest of this lesson. The first four operations listed above are for both text and random access files. The last two just for random access.Random access means we can move to any part of a file and read or write data from it without having to read through the entire file. Back thirty years ago, much data was stored on large reels of computer tape. The only way to get to a point on the tape was by reading all the way through the tape. Then disks came along and now we can read any part of a file directly.On the next page: Programming with Binary FilesA binary file is a file of any length that holds bytes with values in the range 0 to 0xff. (0 to 255). These bytes have no other meaning unlike in a text file where a value of 13 means carriage return, 10 means line feed, 26 means end of file and software reading text files has to deal with these.In modern terms we call binary files a stream of bytes and more modern languages tend to work with streams rather than files.The important part is the data stream rather than where it came from! In C you can think about the data either in terms of files or streams. Or if it helps, think of a file/stream as a very long array! With random access you can read or write to any part of this array. With sequential you have to loop through it from the start like a big tape.DownloadExample 1.This shows a simple binary file being opened for writing, with a text string (char *) being written into it. Normally you'd use a text file for that but I wanted to show that you can write text to a binary file.// ex1.c #include #include int main(int argc, char * argv[]) { const char * filename="test.txt"; const char * mytext="Once upon a time there were three bears."; int byteswritten=0; FILE * ft= fopen(filename, "wb") ; if (ft) { fwrite(mytext,sizeof(char),strlen(mytext), ft) ; fclose( ft ) ; } printf("len of mytext = %i ",strlen(mytext)) ; return 0; } Random Access to file in CRandom access means we can move to any part of a file and read or write data from it without having to read through the entire file. we can access the data stored in the file in two ways.1. Sequentially2. Randomlyif we want to access the forty fourth record then first forty three record read sequentially to reach forty four record. In random access data can be accessed and processed directly .There is no need to read each record sequentially. If we want to access a particular record random access takes less time than the sequential access.C supports these function for random access file.1. fseek( ) Function2. ftell ( ) FunctionHow to use fseek() function in CThis function is used for setting the file position pointer at the specified bytes .fseekis a function belonging to the ANCI C standard Library and included in the file stdio.h. Its purpose is to change the file position indicator for the specified stream.int fseek(FILE *stream_pointer, long offset, int origin);

Argument meaning: stream_pointeris a pointer to the streamFILEstructure of which the position indicator should be changed; offsetis alonginteger which specifies the number of bytes fromoriginwhere the position indicator should be placed; originis an integer which specifies the origin position. It can be: SEEK_SET: origin is the start of the stream. SEEK_CUR: origin is the current position. SEEK_END: origin is the end of the stream./** Program to understand the use of fseek function*/#include#include#includestructemprecord{charname[30];intage;floatsal;}emp;voidmain(){intn;FILE *fp;fp=fopen("employee.dat","rb");if(fp==NULL){printf("/n error in opening file");exit(1);}printf("enter the record no to be read");scanf("%d",&n);fseek(fp,(n-1)*sizeof(emp),0);freed(&emp,sizeof(emp),1,fp);printf("%s\t,emp.name);printf("%d\t",emp.age);printf("%f\n",emp.sal);fclose(fp);getch();};