Watcom C Library Reference : _dos_open, _dos_read, _dos_setblock, _dos_setdate
Watcom C Reference/D - E - F 2021. 6. 22. 12:54
Watcom C Library Reference : _dos_open, _dos_read, _dos_setblock, _dos_setdate
_dos_open
Synopsis : #include <dos.h>
#include <fcntl.h>
#include <share.h>
unsigned _dos_open( char *path, unsigned mode, int *handle );
Description : The _dos_open function uses system call 0x3D to open the file specified by path, which must be an existing file. The mode argument specifies the file's access, sharing and inheritance permissions. The access mode must be one of:
| Mode | Meaning |
| O_RDONLY | Read only |
| O_WRONLY | Write only |
| O_RDWR | Both read and write |
The sharing permissions, if specified, must be one of:
| Permission | Meaning |
| SH_COMPAT | Set compatibility mode. |
| SH_DENYRW | Prevent read or write access to the file. |
| SH_DENYWR | Prevent write access of the file. |
| SH_DENYRD | Prevent read access to the file. |
| SH_DENYNO | Permit both read and write access to the file. |
The inheritance permission, if specified, is:
| Permission | Meaning |
| O_NOINHERIT | File is not inherited by a child process |
Returns : The _dos_open function returns zero if successful. Otherwise, it returns an MS-DOS error code and sets errno to one of the following values:
| Constant | Meaning |
| EACCES | Access denied because path specifies a directory or a volume opening a read-only file for write access |
| EINVAL | A sharing mode was specified when file sharing is not installed access-mode value is invalid |
| EMFILE | No more handles available, (too many open files) |
| ENOENT | Path or file not found |
See Also : _dos_close, _dos_creat, _dos_creatnew, _dos_read, _dos_write, open
Example :
#include <stdio.h>
#include <dos.h>
#include <fcntl.h>
#include <share.h>
void main( )
{
int handle;
if( _dos_open( "file", O_RDONLY, &handle ) != 0 ) {
printf( "Unable to open file\n" );
} else {
printf( "Open succeeded\n" );
_dos_close( handle );
}
}
Classification : DOS
Systems : DOS, Win, OS/2 1.x(all), OS/2 2.x, NT, DOS/PM
_dos_read
Synopsis : #include <dos.h>
unsigned _dos_read( int handle, void __far *buffer, unsigned count, unsigned *bytes );
Description : The _dos_read function uses system call 0x3F to read count bytes of data from the tile specified by handle into the buffer pointed to by buffer. The number of bytes successfully read will be stored in the unsigned integer pointed to by bytes.
Returns : The _dos_read function returns zero if successful. Otherwise, it returns an MS-DOS error code and sets errno to one of the following values:
| Constant | Meaning |
| EACCES | Access denied because the file is not open for read access |
| EBADF | Invalid file handle |
See Also : _dos_close, _dos_open, _dos_write
Example :
#include <stdio.h>
#include <dos.h>
#include <fcntl.h>
void main( )
{
unsigned len_read;
int handle;
auto char buffer[80];
if( _dos_open( "file", O_RDONLY, &handle ) != 0 ) {
printf( "Unable to open file\n" );
} else {
printf( "Open succeeded\n" );
_dos read( handle, buffer, 80, &len_read);
_dos_close( handle );
}
}
Classification : DOS
Systems : DOS, Win, OS/2 1.x(all), OS/2 2.x, NT, DOS/PM
_dos_setblock
Synopsis : #include <dos.h>
unsigned _dos_setblock ( unsigned size, unsigned short segment, unsigned *maxsize );
Description : The _dos_setblock function uses system call 0x4A to change the size of segment was previously allocated by _dos_allocmem, to size paragraphs. If the request fails the maximum number of paragraphs that this memory block can be changed to is returned in the word pointed to by maxsize.
Returns : The _dos_setblock function returns zero if successful. Otherwise, it returns an MS-DOS error code and sets errno to ENOMEM indicating a bad segment value, insufficient memory or corrupted memory.
See Also : _dos_allocmem, _dos_freemem, realloc
Example :
#include <stdio.h>
#include <dos.h>
void main( )
{
unsigned short segment;
unsigned maxsize;
/* Try to allocate 100 paragraphs, then free them */
if( _dos_allocmem ( 100, &segment ) != 0 ) {
printf( "_dos_allocmem failed\n" );
printf( "Only %u paragraphs available\n", segment);
} else {
printf( "_dos_allocmem succeeded\n" );
/* Try to increase it to 200 paragraphs */
if ( _dos_setblock ( 200, segment, &maxsize ) != 0 ) {
printf( "Unable to increase the size\n" );
}
if ( _dos_freemem ( segment ) != 0 ) {
printf( "_dos_freemem failed\n" );
}
}
}
Classification : DOS
Systems : DOS, DOS/PM
_dos_setdate
Synopsis : #include <dos.h>
unsigned _dos_setdate( struct dosdate_t *date );
struct dosdate_t {
unsigned char day; /* 1-31 */
unsigned char month; /* 1-12 */
unsigned short year; /* 1980-2099 */
unsigned char dayofweek; /* 0-6 (0-Sunday) */
};
Description : The _dos_setdate function uses system call 0x2B to set the current system date. The date information is passed in a dosdate_t structure pointed to by date.
Returns : The _dos_setdate function returns zero if successful. Otherwise, it returns a non-zero value and sets errno to EINVAL indicating that an invalid date was given.
See Also : _dos_getdate, _dos_gettime, _dos_settime, gmtime, localtime, mktime, time
Example :
#include <stdio.h>
#include <dos.h>
void main( )
{
struct dosdate_t date;
struct dostime_t time;
/* Get and display the current date and time */
_dos_getdate( &date );
_dos_gettime ( &time);
printf( "The date (MM-DD-YYYY) is : %d-%d-%d\n", date.month, date.day, date.year);
printf( "The time (HH:MM:SS) is : %.2d:%.2d:%.2d\n", time , hour, time.minute, time.second );
/* Change it to the turn of the century */
date.year = 1999;
date.month = 12;
date.day = 31;
time.hour = 23;
time.minute = 59;
_dos_setdate( &date );
_dos_settime ( &time );
printf( "New date (MM-DD-YYYY) is : %d-%d-%d\n", date.month, date.day, date.year );
printf( "New time (HH:MM:SS) is : %.2d:%.2d:%.2d\n", time. hour, time.minute, time.second );
}
produces the following:
The date (MM-DD-YYYY) is : 12-25-1989
The time (HH:MM:SS) is : 14:23:15
New date (MM-DD-YYYY) is : 12-31-1999
New time (HH:MM:SS) is : 23:59:59
Classification : DOS
Systems : DOS, Win, OS/2 1.x(all), OS/2 2.x, NT, DOS/PM
This manual describes the WATCOM C library for DOS, Windows, and OS/2, It includes the Standard C Library (as defined in the ANSI C Standard).
WATCOM C Language Reference manual describes the ANSI C Programming language and extensions to it which are supported by WATCOM C/C++ (32bit)
