Watcom C Library : locking, log, log10, log2, longjmp
Watcom C Reference/K - L- M - N 2021. 7. 11. 17:31
Watcom C Library Reference : locking, log, log10, log2, longjmp
locking
Synopsis : #include <sys\locking.h>
int locking( int handle, int mode, long nbyte );
Description : The locking function locks or unlocks nbyte bytes of the file specified by handle. Locking a region of a file prevents other processes from reading or writing the locked region until the region has been unlocked. The locking and unlocking takes place at the current file position. The argument mode specifies the action to be performed. The possible values for mode are:
| Mode | Meaning |
| LK_LOCK | Locks the specified region. The function will retry to lock the region after 1 second intervals until successful or until 10 attempts have been made. |
| LK_RLCK | Same action as LK_LOCK. |
| LK_NBLCK | Non-blocking lock: makes only 1 attempt to lock the specified region. |
| LK_NBRLCK | Same action as LK_NBLCK. |
| LK_UNLCK | Unlocks the specified region. The region must have been previously locked. |
Multiple regions of a file can be locked, but no overlapping regions are allowed. You cannot unlock multiple regions in the same call, even if the regions are contiguous. All locked regions of a file should be unlocked before closing a file or exiting the program.
With DOS, locking is supported by version 3.0 or later. Note that SHARE.COM or SHARE.EXE must be installed.
Returns : The locking function returns zero if successful. Otherwise, it returns -1 and errno is set to indicate the error.
Errors : When an error has occurred, errno contains a value indicating the type of error that has been detected.
| Constant | Meaning |
| EACCES | Indicates a locking violation (file already locked or unlocked). |
| EBADF | Indicates an invalid file handle. |
| EDEADLOCK | Indicates a locking violation. This error is returned when mode is LK_LOCK or LK_RLCK and the file cannot be locked after 10 attempts. |
| EINVAL | Indicates that an invalid argument was given to the function. |
See Also : creat, _dos_creat, _dos_open, lock, open, sopen, unlock
Example :
#include <stdio.h>
#include <sys\locking.h>
#include <share.h>
#include <fcntl.h>
#include <io.h>
void main( )
{
int handle;
unsigned nbytes;
unsigned long offset;
auto char buffer[512];
nbytes = 512;
offset = 1024;
handle = sopen( "db.fil", O_RDWR, SH_DENYNO );
if( handle != -1 ) {
lseek( handle, offset, SEEK_SET );
locking( handle, LK_LOCK, nbytes );
read( handle, buffer, nbytes);
/* update data in the buffer */
lseek( handle, offset, SEEK_SET );
write( handle, buffer, nbytes );
lseek( handle, offset, SEEK_SET );
locking( handle, LK_UNLCK, nbytes );
close( handle );
}
}
Classification : WATCOM
Systems : All
log
Synopsis : #include <math.h>
double log( double x );
Description : The log function computes the natural logarithm (base e) of x. A domain error occurs if argument is negative. A range error occurs if the argument is zero.
Returns : The log function returns the natural logarithm of the argument. When the argument is outside the permissible range, the matherr function is called. Unless the default matherr function is replaced, it will set the global variable errno to EDOM, and print a "DOMAIN error" diagnostic message using the stderr stream.
See Also : exp, log10, log2, pow, matherr
Example :
#include <stdio.h>
#include <math.h>
void main( )
{
printf( "%f\n", log(.5) );
}
produces the following :
-0.693147
Classification : ANSI
Systems : All
log10
Synopsis : #include <math.h>
double log10( double x );
Description : The log10 function computes the logarithm (base 10) of x. A domain error occurs if the argument is negative. A range error occurs if the argument is zero.
Returns : The log10 function returns the logarithm (base 10) of the argument. When the argument is outside the permissible range, the matherr function is called. Unless the default matherr function is replaced, it will set the global variable errno to EDOM, and print a "DOMAIN error" diagnostic message using the stderr stream.
See Also : exp, log, log2, pow, matherr
Example :
#include <stdio.h>
#include <math.h>
void main( )
{
printf( "%f\n", log10(.5) );
}
produces the following :
-0.301030
Classification : ANSI
Systems : All
log2
Synopsis : #include <math.h>
double log2( double x );
Description : The log2 function computes the logarithm (base 2) of x. A domain error occurs if the argument is negative. A range error occurs if the argument is zero.
Returns : The log2 function returns the logarithm (base 2) of the argument. When the argument is outside the permissible range, the matherr function is called. Unless the default matherr function is replaced, it will set the global variable errno to EDOM, and print a "DOMAIN error" diagnostic message using the stderr stream.
See Also : exp, log, log10, pow, matherr
Example :
#include <stdio.h>
#include <math.h>
void main( )
{
printf( "%f\n", log2 (.25) );
}
produces the following :
-2.000000
Classification : WATCOM
Systems : All
longjmp
Synopsis : #include <setjmp.h>
void longjmp( jmp_buf env, int return_value );
Description : The longjmp function restores the environment saved by the most recent call to the setjmp function with the corresponding jmp_buf argument.
Returns : After the longimp function restores the environment, program execution continues as if the corresponding call to setjmp had just returned the value specified by return_value. If the value of return_value is 0, the value returned is 1.
See Also : setjmp
Example :
#include <stdio.h>
#include <setjmp.h>
jmp_buf env;
rtn( )
{
printf( "about to longjmp \n" );
longjmp( env, 14 );
}
void main( )
{
int ret_val = 293;
if( 0 == ( ret_val = setjmp( env ) ) ) {
printf( "after setjmp %d\n", ret_val );
rtn( );
printf( "back from rtn %d\n", ret_val );
} else {
printf( "back from longjmp %d\n", ret_val );
}
}
produces the following :
after setjmp 0
about to longjmp
back from longjmp 14
Classification : ANSI
Systems : All
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)
