Merge pull request #183 from chrboesch/hello_c

added the first C exercise

build.zig

@@ -31,6 +31,10 @@ const Exercise = struct {
     /// We need to keep track of this, so we compile without the self hosted compiler
     @"async": bool = false,
 
+    /// This exercise makes use of C functions
+    /// We need to keep track of this, so we compile with libc
+    C: bool = false,
+
     /// Returns the name of the main file with .zig stripped.
     pub fn baseName(self: Exercise) []const u8 {
         assert(std.mem.endsWith(u8, self.main_file, ".zig"));
@@ -465,6 +469,11 @@ const exercises = [_]Exercise{
         .main_file = "092_interfaces.zig",
         .output = "Daily Insect Report:\nAnt is alive.\nBee visited 17 flowers.\nGrasshopper hopped 32 meters.",
     },
+    .{
+        .main_file = "093_hello_c.zig",
+        .output = "Hello C from Zig! - C result ist 17 chars",
+        .C = true,
+    },
     .{
         .main_file = "999_the_end.zig",
         .output = "\nThis is the end for now!\nWe hope you had fun and were able to learn a lot, so visit us again when the next exercises are available.",
@@ -729,6 +738,11 @@ const ZiglingStep = struct {
         //     zig_args.append("-fstage1") catch unreachable;
         // }
 
+        // Enable C support for exercises that use C functions
+        if (self.exercise.C) {
+            zig_args.append("-lc") catch unreachable;
+        }
+
         if (builder.color != .auto) {
             zig_args.append("--color") catch unreachable;
             zig_args.append(@tagName(builder.color)) catch unreachable;

exercises/093_hello_c.zig

@@ -0,0 +1,68 @@
+//
+// When Andrew Kelley announced the idea of a new programming language
+// - namely Zig - in his blog on February 8, 2016, he also immediately
+// stated his ambitious goal: to replace the C language!
+//
+// In order to be able to achieve this goal at all, Zig should be
+// as compatible as possible with its "predecessor".
+// Only if it is possible to exchange individual modules in existing
+// C programs without having to use complicated wrappers,
+// the undertaking has a chance of success.
+//
+// So it is not surprising that calling C functions and vice versa
+// is extremely "smooth".
+//
+// To call C functions in Zig, you only need to specify the library
+// that contains said function. For this purpose there is a built-in
+// function corresponding to the well-known @import():
+//
+//                           @cImport()
+//
+// All required libraries can now be included in the usual Zig notation:
+//
+//                    const c = @cImport({
+//                        @cInclude("stdio.h");
+//                        @cInclude("...");
+//                    });
+//
+// Now a function can be called via the (in this example) constant 'c':
+//
+//                    c.puts("Hello world!");
+//
+// By the way, most C functions have return values in the form of an
+// integer value. Errors can then be evaluated (return < 0) or other
+// information can be obtained. For example, 'puts' returns the number
+// of characters output.
+//
+// So that all this does not remain a dry theroy now, let's just start
+// and call a C function out of Zig.
+
+// our well-known "import" for Zig
+const std = @import("std");
+
+// and here the new the import for C
+const c = @cImport({
+    @cInclude("unistd.h");
+});
+
+pub fn main() void {
+
+    // In order to output a text that can be evaluated by the
+    // Zig Builder, we need to write it to the Error output.
+    // In Zig we do this with "std.debug.print" and in C we can
+    // specify a file descriptor i.e. 2 for error console.
+    //
+    // In  this exercise we use 'write' to output 17 chars,
+    // but something is missing...
+    const c_res = write(2, "Hello C from Zig!", 17);
+
+    // let's see what the result from C is:
+    std.debug.print(" - C result ist {d} chars\n", .{c_res});
+}
+//
+// Something must be considered when compiling with C functions.
+// Namely that the Zig compiler knows that it should include
+// corresponding libraries. For this purpose we call the compiler
+// with the parameter "lc" for such a program,
+// e.g. "zig run -lc hello_c.zig".
+//

patches/patches/093_hello_c.patch

@@ -0,0 +1,4 @@
+57c57
+<     const c_res = write(2, "Hello C from Zig!", 17);
+---
+>     const c_res = c.write(2, "Hello C from Zig!", 17);