vb.net barcode font 10: Working with Files in Java

Drawing Data Matrix in Java 10: Working with Files

CHAPTER 10: Working with Files
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Once we finish writing the linked list into the file, we ll close the file by calling fclose():
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fclose( fp ); } ReadFile() starts by opening the file dvdData for reading. If we can t open the file, we ll
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print an error message and return, leaving the list empty:
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/****************************> ReadFile <*/ void ReadFile( void ) { FILE *fp; struct DVDInfo *infoPtr; if ( ( fp = fopen( kDVDFileName, "r" ) ) == NULL ) { printf( "***ERROR: Could not read DVD file!" ); return; }
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With the file open, we ll enter a loop that continues as long as ReadStructFromFile() returns true. By using the do-while loop, we ll execute the body of the loop before we call ReadStructFromFile() for the first time. This is what we want. The body of the loop attempts to allocate a block of memory the size of a DVDInfo struct. If the malloc() fails, we ll bail out of the program.
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do { infoPtr = malloc( sizeof( struct DVDInfo ) ); if ( NULL == infoPtr ) { printf( "Out of memory!!! exit( 0 ); }
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Goodbye!\n" );
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} while ( ReadStructFromFile( fp, infoPtr ) ); ReadStructFromFile() will return false when it hits the end of the file, when it can t read
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another set of DVDInfo fields. In that case, we ll close the file and free up the last block we just allocated, since we have nothing to store in it:
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fclose( fp ); free( infoPtr ); } ReadStructFromFile() uses a funky form of fscanf() to read in the first two DVDInfo fields. Notice the use of the format descriptor "%[^\n]\n". This tells fscanf() to read characters from the specified file until it hits a '\n' and then to read the '\n' character and stop. The characters [^\n] represent the set of all characters except '\n'. Note that the %[ format specifier places a terminating zero byte at the end of the characters it reads in.
CHAPTER 10: Working with Files
/*******************> ReadStructFromFile <*/ char ReadStructFromFile( FILE *fp, struct DVDInfo *infoPtr ) { int num; if ( fscanf( fp, "%[^\n]\n", infoPtr->title ) != EOF ) {
NOTE
The square brackets inside a format specifier give you much greater control over scanf(). For example, the format specifier "%[abcd]" would tell scanf() to keep reading as long as it was reading 'a', 'b', 'c', or 'd'. The first non-[abcd] character would be left in the input buffer for the next part of the format specifier or for the next read operation to pick up. If the first character in the set is the character ^, the set represents the characters that do not belong to that set. In other words, the format specifier "%[^abdvd]", tells scanf() to continue reading as long as it doesn t encounter any of the characters 'a', 'b', 'c', or 'd'.
If fscanf() hits the end of the file, we ll return false, letting the calling function know there are no more fields to read. If fscanf() succeeds, we ll move on to the comment field using the same technique. If this second fscanf() fails, we ve got a problem, since we read a title but couldn t read a comment:
if ( fscanf( fp, "%[^\n]\n", infoPtr->comment ) == EOF ) { printf( "Missing DVD comment!\n" ); return false; }
You may have noticed that ReadStructFromFile() returns a char instead of a bool. Since true and false are integer values, char, short, or int will work. Personally, I think you should stick with the convention of declaring a function as bool if it strictly returns true or false Since much of the code you encounter will use the int returning true or false approach, I thought you should see this for yourself. Assuming we got both the title and comment, we ll use a more normal format specifier to pick up an int and the third carriage return:
else if ( fscanf( fp, "%d\n", &num ) == EOF ) { printf( "Missing DVD rating!\n" ); return false; }
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