QMReadu() |
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The QMReadu() function reads a record with an exclusive update lock.
Format
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The QMReadu() function requests the server to return the record with key Id from the file opened as FileNo. An exclusive update lock is applied to the record. Only one user may hold an exclusive update lock on any one record at one time. An exclusive update lock also cannot be obtained if another user holds a shareable read lock on the record or a file lock on the entire file.
If the action is blocked by a lock held by another user, the function returns a null string and the Errno variable is set to SV_LOCKED. The QMStatus() function can be used to retrieve the user number of the process holding the lock.
If successful, the function returns the record as a dynamic array string and the Errno variable is set to SV_OK. The record is locked by the server process.
If the record cannot be found, the function returns a null string and the Errno variable is set to SV_ELSE. The QMStatus() function can be used to retrieve the error number. The record is locked by the server process to allow creation of the record. If the lock is not required, it should be released using the QMRelease() function.
Conditions that would normally cause a QMBasic program to abort or to take the ON ERROR clause of a READ statement return a null string and the Errno variable is set to SV_ON_ERROR. The QMStatus() function can be used to retrieve the error number.
In the C API library, the dynamic memory allocated for the returned string must subsequently be freed by the calling program. |