Basic Random Files Compatible with C Random (Binary) Files (62057)

MORE INFORMATION

Versions of QuickBasic earlier than 4.00 use Microsoft Binary format (MBF) for floating-point numbers. Current versions of the C compiler expect floating-point numbers to be stored in IEEE format. Therefore, current versions of C cannot easily read random access files that are created with QuickBasic versions 1.00, 1.01, 1.02, 2.00, 2.01, and 3.00 if those files contain single- or double-precision numbers.

Both Basic and C store random access file records as byte-per-byte copies of the record variable written to the file. No "extra" information about the data is stored along with the record. A direct image of the record variable is copied to the record on disk. Therefore, because Basic and C have many data types in common, it is a straightforward process to create records in C that are the equivalent of Basic records. The following table summarizes what C data type you would use in a "struct" to mirror the data type in a Basic TYPE.

   Basic TYPE Data Type   C struct Data Type
   --------------------   ------------------
   INTEGER                int
   LONG                   long
   SINGLE                 float
   DOUBLE                 double
   STRING * n             char array[]
				

The only precaution is that all strings passed from Basic to C in a TYPE should have a null character (CHR$(0)) as the last character if any C string-manipulation functions are going to be used.

The following Basic example shows writing both a TYPEd record and a FIELDed record to a Basic random access file. The following C program can then be used to read and display the contents of the two files created with Basic. The Basic program should be compiled with QuickBasic version 4.00, 4.00b, or 4.50, Microsoft Basic Compiler version 6.00 or 6.00b, or Basic PDS version 7.00 or 7.10. The C program should be compiled with C version 5.00 or 5.10, or with QuickC version 1.00, 1.01, 2.00, 2.01, 2.50, or 2.51.

Code Example

'******************************  Basic ***************************

TYPE rec1
   s1 AS SINGLE
   d1 AS DOUBLE
   i1 AS INTEGER
   l1 AS LONG
END TYPE

DIM var1 AS rec1
var1.s1 = 1.1: var1.d1 = 2.2: var1.i1 = 3: var1.l1 = 4

OPEN "type.dat" FOR RANDOM AS #1
PUT 1, 1, var1

OPEN "field.dat" FOR RANDOM AS #2 LEN = LEN(var1)
FIELD #2, 4 AS single1$, 8 AS double1$, 2 AS int1$, 4 AS long1$
LSET single1$ = MKS$(var1.s1)
LSET double1$ = MKD$(var1.d1)
LSET int1$ = MKI$(var1.i1)
LSET long1$ = MKL$(var1.l1)
PUT 2, 1
CLOSE
END

/************************************************************/ 
/*                            C Program                     */ 
/************************************************************/ 

#include <stdio.h>
typedef struct {
  float     float1;
  double    double1;
  int       int1;
  long int  long1;
} RECORD;

void printit(RECORD * rec1);

void
main(void)
{

   FILE * TYPEdfile  = NULL;
   FILE * FIELDfile = NULL;
   int NumRead;
   RECORD rec1;

   TYPEdfile = fopen("TYPE.DAT","r");
   if(TYPEdfile == NULL) {
        printf("Open fail on single.dat\n");
    }
   else {
        NumRead = fread(&rec1,sizeof(rec1),1,TYPEdfile);
        if (NumRead ==  0) printf("Failed to read double.dat\n");
        printf("Contents of random file created with TYPE: \n");
        printit(&rec1);
    }

   FIELDfile = fopen("FIELD.DAT","r");
   if(FIELDfile == NULL) {
        printf("Open fail on field.dat\n");
     }
   else {
        printf("Contents of random file created with FIELD: \n");
        NumRead = fread(&rec1,sizeof(rec1),1,FIELDfile);
        printit(&rec1);
     }

   fcloseall();
}

void printit(RECORD * rec1)
{
   printf("%f\n",   rec1->float1);
   printf("%lf\n",  rec1->double1);
   printf("%d\n",   rec1->int1);
   printf("%ld\n\n",rec1->long1);
}