fullfile — Build platform-correct file paths from path segments in MATLAB and RunMat.
fullfile joins path segments using the platform-specific separator to produce a single path string. It accepts any number of segments and returns a character row vector, with separator normalization and empty-segment handling matching MATLAB semantics.
Syntax
file = fullfile(part1)
file = fullfile(part1, part2, ...)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
part1 | StringScalar | Yes | — | First path component. |
partN | StringScalar | Variadic | — | Additional path components. |
Returns
| Name | Type | Description |
|---|---|---|
file | StringScalar | Platform-correct joined path. |
Errors
| Identifier | When | Message |
|---|---|---|
| — | No path arguments are supplied. | fullfile: not enough input arguments |
| — | A path argument is not a character vector, string scalar/array scalar, or tensor of character codes. | fullfile: arguments must be character vectors or string scalars |
How fullfile works
fullfile(part1, part2, ...)joins the inputs with the platform file separator (/on macOS and Linux,\on Windows).- Absolute path segments reset the accumulated path, mirroring MATLAB and OS path rules.
- Empty segments are ignored, so
fullfile("", "data")returnsdata. - Inputs must be character vectors or string scalars. Single-element string arrays are accepted. Other input types raise
fullfile: arguments must be character vectors or string scalars. - The output is a character vector. Wrap the result with
string(...)if you prefer string scalars.
Does RunMat run fullfile on the GPU?
fullfile performs string manipulation on the CPU only. Any GPU-resident inputs are gathered to the host before path assembly so the resulting character vector is always in CPU memory.
GPU memory and residency
No. fullfile is a host-side path builder. GPU-resident text inputs are gathered automatically, so there is no benefit to keeping path strings on the GPU.
Examples
Join Relative Path Segments
p = fullfile("data", "raw", "sample.dat")Expected output:
p =
data/raw/sample.datUse fullfile With pwd
root = pwd;
config = fullfile(root, "config", "settings.json")Expected output:
% Returns a full path rooted at the current working folderBuild A Subfolder Path
logDir = fullfile("logs", "2026");
status = mkdir(logDir)Expected output:
status =
1Create A File In A Nested Folder
mkdir(fullfile("data", "raw"));
fid = fopen(fullfile("data", "raw", "sample.dat"), "w");
fclose(fid)Expected output:
% Creates data/raw/sample.datUsing fullfile with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how fullfile changes the result.
Run a small fullfile example, explain the result, then change one input and compare the output.
FAQ
Why does fullfile return a character vector instead of a string?⌄
MATLAB returns character vectors for fullfile. RunMat mirrors that behavior for compatibility; use string(fullfile(...)) if you prefer string scalars.
Does fullfile expand ~ to the home directory?⌄
No. fullfile performs string assembly only. Use cd or filesystem APIs that expand ~ when you need home expansion.
What happens if a segment is absolute?⌄
Absolute segments reset the accumulated path, matching MATLAB and OS path rules.
Can I pass numeric character codes?⌄
Yes. Numeric arrays that represent character codes are accepted as long as they form a row vector, just like other RunMat text inputs.
Does fullfile run on the GPU?⌄
No. It is a host-only utility and gathers GPU-resident inputs before processing.
Related Io functions
Repl Fs
addpath · cd · copyfile · delete · dir · exist · fileattrib · fileparts · 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
Filetext
fclose · feof · fgetl · fgets · fileread · filewrite · fopen · fprintf · fread · frewind · fwrite · readlines · writelines
Import
Json
Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how fullfile is executed, line by line, in Rust.
- View the source for fullfile in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
RunMat is an open-source runtime that executes MATLAB-syntax code blazing on any GPU. It is licensed under the Apache 2.0 license.
- RunMat automatically optimizes your math for GPU execution on Apple, Nvidia, and AMD hardware. No code changes needed. Simulations that took hours now take minutes.
- Start running code in seconds. RunMat runs in the browser, on the desktop, or from the CLI. No license server, no IT ticket.