1. C Programming
Language
By:
Yogendra Pal
yogendra@learnbywatch.com
Dedicated to My mother and Father

2. t
y
Keep your notebook with you.
Write important point and questions that comes in your mind
Solve Mind band exercise.
C
Rewind when not clear
Ask Questions by call or SMS or by mail
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THIS IS FILE I/O
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3. File…
• Files are used to store data to disks.
• Data on disk is permanent.
• Variables are stored on RAM only.
• Data on RAM can not be accessed later.
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4. File…
• File : Group of related records.
Sonu 001 04/02
Amit 002 09/05
File
Asif 003 10/09
Hari 004 30/11
Sonu 001 04/02 Record
Sonu Field
1001001 byte
1 bit
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5. Files in C
• A file is a sequence of bytes.
– File ends with End Of File (EOF) marker.
• Streams are used to communicate with file.
stream
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6. File
• Use FILE pointer to access a file.
FILE *fp;
• fopen() library function is used to open a file.
– fopen( file_path, open_mode);
– Returns NULL if file can not open.
• fclose() library function is used to close a file.
– fclose(file_pointer);
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7. File open mode
Mode Description
r Open a file for reading.
w Create a file for writing. If the file already exists, discard the current contents.
a Append; open or create a file for writing at end of file.
r+ Open a file for update (reading and writing).
w+ Create a file for update. If the file already exists, discard the current contents.
a+ Append; open or create a file for update; writing is done at the end of the file.
rb Open a file for reading in binary mode.
wb Create a file for writing in binary mode. If the file already exists, discard the current contents.
ab Append; open or create a file for writing at end of file in binary mode.
rb+ Open a file for update (reading and writing) in binary mode.
wb+ Create a file for update in binary mode. If the file already exists, discard the current contents.
ab+ Append; open or create a file for update in binary mode; writing is done at the end of the file.
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8. Read / Write a file
• fgetc() : reads one character from a file.
• fputc() : write one character to a file.
• fgets() : read a line (Srring) from a file.
• fputs() : Write a line to a file.
• fprintf() : used to print to a file.
• fscanf() : used to read from a file.
• feof() : return true if EOF find.
• rewind() : set file position pointer to the start.
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9. Problem
• Write a program to read a file and print it on
monitor.
• Write a program to create a copy of a file.
• Modify first problem: stop printing if a ‘z’
occurs in file.
• Write a program to create a file.
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10. Sequential Access File
• Write or Read data sequentially.
• Data can not modify without destroying.
• Fields can vary in size.
fopen(“one.dat”, “w”);
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11. Random Access File
• Access any record without searching through
other records.
• Data can be inserted without destroying other
data.
• Implemented using fixed length records.
fopen(“one.dat”, “wb”);
• Also known as binary file.
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12. Random Access File…
• fwrite() : used to write to binary file.
• fread() : read from binary file.
• fseek(): Used to set the file position pointer to
a specific location.
• Operation sequention.
– Open/Create->seek->Write.
– Open->seek->Read.
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13. fwrite() / fread()
• fwrite(&data,sizeof(data),1,fp);
• data : data that you want to write to file.
• sizeof(data) : number of bytes to write.
• 1 : for arrays, number of elements to write.
• fp : file to write.
– fread(&data,sizeof(data),1,fp);
• &data : variable to store data.
• sizeof(data) : number of bytes to read.
• 1 : for arrays, number of elements to read.
• fp : file from read.
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14. fseek()
• fseek(fp,offset,symbolic_constant);
– fp : File pointer.
– offset : location of file position pointer.
– symbolic_constant : specify where in file we are
reading from.
• SEEK_SET: beginning of file.
• SEEK_CUR: current location in file.
• SEEK_END: end of file.
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For any problem in this tutorial mail me at
yogendra@learnbywatch.com
with the subject “C”
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