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zig: use a c library from a dependency

Learn how to seamlessly integrate C libraries, specifically focusing on cJSON, into your Zig projects by leveraging zig fetch and modifying your build.zig file.
zig: use a c library from a dependency

The zig community is large, but the number of native zig libraries is still growing. However, you can easily import any C library into your zig project.

Step 1: Fetch and Install the C Library

First install the c library, we will use cJSON as an example.

zig fetch --save=cjson https://github.com/DaveGamble/cJSON/archive/refs/heads/master.zip

Step 2: Modify build.zig to Include the C Library

Now we need to adjust build.zig to import the library to our executable:

// ...
const cjsonDep = b.dependency("cjson", .{});
exe.addIncludePath(cjsonDep.path(""));
exe.linkLibC();
exe.addCSourceFiles(.{
    .root = .{
        .dependency = .{
            .dependency = cjsonDep,
            .sub_path = "",
        },
    },
    .files = &[_][]const u8{
        "cJSON.c",
    },
});
// ...

Step 3: Use the C Library in Your zig Application

Now, you can access the public API of cJSON in your zig application.

const c = @cImport({
    @cInclude("cJSON.h");
});
 
const value = c.cJSON_Parse(
    "{ \"name\": \"Patrick\" }",
);
defer std.c.free(value);
const name = c.cJSON_GetObjectItemCaseSensitive(
    value,
    "name",
);
defer std.c.free(name);
if (c.cJSON_IsString(name) == 1) {
    const str: [:0]u8 = std.mem.span(name.*.valuestring);
    std.debug.print(
        "name = {s}, len = {d}\n",
        .{
            str,
            str.len,
        },
    );
}

Output:

> zig build run
name = Patrick, len = 7

With this approach, you can easily extend your Zig applications using the vast ecosystem of C libraries, like cJSON. This flexibility allows you to bridge the gap between Zig and C seamlessly.

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