fclose — Close file identifiers in MATLAB and RunMat.
fclose closes files previously opened with fopen. MATLAB-compatible mode accepts one scalar double file identifier or the character vector 'all' and returns at most one double status. RunMat's collection, typed-integer, logical, string, resident, no-input, and diagnostic-message forms are separately gated extensions.
Syntax
status = fclose()
status = fclose(fid)
status = fclose("all")
[status, msg] = fclose(...)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
fid | Any | Yes | — | File identifier scalar, vector, cell list, or keyword "all". |
mode | StringScalar | Yes | "all" | Close all open user file identifiers. |
Returns
| Name | Type | Description |
|---|---|---|
status | NumericScalar | 0 on success, -1 on failure. |
msg | StringScalar | Failure message when status is -1. |
Returned values from fclose depend on how many outputs the caller requests.
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:fclose:InvalidInput | Input argument count or file identifier value/type is invalid. | fclose: invalid input arguments |
RunMat:fclose:InvalidIdentifier | The provided file identifier does not refer to an open file. | fclose: invalid file identifier. Use fopen to generate a valid file ID. |
RunMat:fclose:IoFailure | Closing an open file failed due to I/O error. | fclose: failed to close file |
| — | Internal runtime control-flow or conversion failed. | fclose: internal error |
How fclose works
status = fclose(fid)closes the file represented by the numeric identifierfid. The status is0on success and-1if the identifier is invalid.status = fclose('all')closes every open file except the standard streams (0, 1, 2). The documented keyword is a character vector.- The file identifier must be a finite, integer-valued scalar double in MATLAB-compatible mode. RunMat validates the complete request before performing a close.
- Typed integer identifiers, identifier collections, logical identifiers, string-scalar
'all', resident identifiers,fclose()with no input, and[status, message]are available only when their RunMat extensions are enabled. - Identifiers 0, 1, and 2 refer to standard input, output, and error.
fclosetreats them as already-open handles and simply returns success. - RunMat keeps file metadata in a registry shared with
fopen, ensuring MATLAB-compatible behaviour across subsequent I/O builtins.
Does RunMat run fclose on the GPU?
fclose does not perform GPU computation. A resident numeric identifier is rejected before provider lookup in MATLAB-compatible mode. With the resident-fileID extension enabled, RunMat gathers it through its owning provider and then dispatches the host-only close logic.
Examples
Close a file after writing data
[fid, msg] = fopen('results.txt', 'w');
if fid == -1
error('Failed to open file: %s', msg);
end
fprintf(fid, 'Simulation complete\n');
status = fclose(fid)Expected output:
status = 0Close all open files at once
% Close every file except stdin/stdout/stderr
status = fclose('all')Expected output:
status = 0Handle invalid file identifiers gracefully
status = fclose(9999);
if status == -1
fprintf('Close failed\n');
endExpected output:
status = -1Using fclose with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how fclose changes the result.
Run a small fclose example, explain the result, then change one input and compare the output.
FAQ
What values can I pass to fclose?⌄
For MATLAB-compatible code, pass one scalar double identifier returned by fopen, or the character vector 'all'. Other accepted RunMat forms are explicit extensions.
What does the status code mean?⌄
0 indicates success and -1 indicates failure. MATLAB-compatible mode exposes that single status output; RunMat's diagnostic second output is extension-gated.
Does fclose close standard input/output?⌄
Identifiers 0, 1, and 2 always refer to the process standard streams. fclose accepts them but leaves the streams open, returning a success status.
Can I call fclose multiple times on the same identifier?⌄
Yes. The first call closes the file and subsequent calls return status -1 with the message "Invalid file identifier. Use fopen to generate a valid file ID."
Does fclose flush buffered writes?⌄
Closing a file flushes buffered writes and releases the underlying operating system descriptor, matching MATLAB behaviour.
Do I need to close files explicitly when using GPU arrays?⌄
Yes. GPU residency does not change the lifecycle of file handles. Use fclose to release identifiers created with fopen regardless of where the arguments reside.
Can fclose close files opened by other processes?⌄
No. It only closes identifiers that the current RunMat process opened via fopen.
Related Io functions
Filetext
feof · fgetl · fgets · fileread · filewrite · fopen · fprintf · fread · frewind · fwrite · readlines · writelines
Repl Fs
addpath · cd · copyfile · delete · dir · exist · fileattrib · fileparts · fullfile · genpath · getenv · getpref · isenv · isfile · isfolder · ispref · ls · matlabroot · memmapfile · mkdir · movefile · open · opentoline · path · pathsep · pcode · pwd · readstruct · rehash · restoredefaultpath · rmdir · rmpath · run · savepath · setenv · setpref · system · tempdir · tempname · uigetdir · uigetfile · uiputfile · unsetenv · userpath · what · winqueryreg · xmlread · xmlwrite
Tabular
arrayDatastore · csvread · csvwrite · detectImportOptions · dlmread · dlmwrite · fileDatastore · parquetDatastore · parquetinfo · parquetread · readcell · readmatrix · readtable · readtimetable · spreadsheetImportOptions · writecell · writematrix · writetable · writetimetable · xlsread · xlswrite
Import
Json
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how fclose is executed, line by line, in Rust.
- View the source for fclose in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
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