What is the easiest way to check if a file exists in zig?
As part of my build process, I need to avoid writing over a file if it already exists.
I have seen std.fs.access but I'm not sure if there is an easier way.
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1 Answer
Yes, the std.fs.Dir.access is the one you should use. But for your case, you might want to create the file with the exclusive=true flag and handle the PathAlreadyExists error as recommended in the std.fs.Dir.access documentation:
Be careful of Time-Of-Check-Time-Of-Use race conditions when using this function. For example, instead of testing if a file exists and then opening it, just open it and handle the error for file not found.
For example:
const std = @import("std");
pub fn main() !void {
try write_cache_file();
}
fn write_cache_file() !void {
var file = std.fs.cwd().createFile("file.tmp", .{ .exclusive = true }) catch |e|
switch (e) {
error.PathAlreadyExists => {
std.log.info("already exists", .{});
return;
},
else => return e,
};
defer file.close();
std.log.info("write file here", .{});
}
This prints:
$ zig build run
info: write file here
$ zig build run
info: already exists
3 Comments
tuket
I don't really want to open the file. The idea is
if(!fileExists(filePath)) continueTheBuildProcess_and_copyTheResultingFile(filePath). Should I go with the access approach then?
sigod
@tuket yes. What else do you have in mind?
tuket
That's all, just wanted to be sure. Thank you!