TAILIEUCHUNG - Lecture Introduction to Computer Programming - Lecture 29

The contents of this chapter include all of the following: Collections provided in namespace, collections store object reference, traversal supported, ArrayList can be sorted. | CSC141- Introduction to Computer Programming Teacher: AHMED MUMTAZ MUSTEHSAN Lecture – 29 Thanks for Lecture Slides: 1 File Processing (Continued) 2 Random-Access Files Random access files Access individual records without searching through other records Instant access to records in a file Data can be inserted without destroying other data Data previously stored can be updated or deleted without overwriting Implemented using fixed length records Sequential files do not have fixed length records 0 200 300 400 500 byte offsets } } } } } } } 100 100 bytes 100 bytes 100 bytes 100 bytes 100 bytes 100 bytes 3 Creating a Randomly Accessed File Data in random access files Unformatted (stored as "raw bytes") All data of the same type (int, for example) uses the same amount of memory All records of the same type have a fixed length Data not human readable 4 Creating a Randomly Accessed File Unformatted I/O functions fwrite Transfer bytes from a location in memory to a file fread Transfer bytes from a file to a location in memory Example: fwrite( &number, sizeof( int ), 1, myPtr ); &number – Location to transfer bytes from sizeof( int ) – Number of bytes to transfer 1 – For arrays, number of elements to transfer In this case, "one element" of an array is being transferred myPtr – File to transfer to or from 5 Creating a Randomly Accessed File Writing structs fwrite( &myObject, sizeof (struct myStruct), 1, myPtr ); sizeof – returns size in bytes of object in parentheses To write several array elements Pointer to array as first argument Number of elements to write as third argument 6 /* Fig. : #include /* clientData structure definition */ struct clientData { int acctNum; /* account number */ char lastName[ 15 ]; /* account last name */ char firstName[ 10 ]; /* account first name */ double balance; /* account balance */ }; /* end structure clientData */ int main( void ) { int i;

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