metacritical · May 25, 2024 08:25 · Sep 26, 2017 · Sep 26, 2017 · Sep 26, 2017 · Sep 26, 2017
diff --git a/000_HOWTO.md b/000_HOWTO.md
@@ -14,8 +14,8 @@ crystal build --release --cross-compile --prelude ./no_main library.cr
 
 ```
 gcc library.o -o libfoo.so -rdynamic -shared -lpcre -lgc -lpthread /usr/lib/crystal/ext/libcrystal.a -levent -lrt -ldl -L/usr/lib -L/usr/local/lib
-                                 ^ Add this to link into a shared lib
-             ^ We want a decent name for the shared lib too.
+                                     ^ Add this to link into a shared lib
+              ^ We want a decent name for the shared lib too.
 ```
 
 * Build and link the C program:

diff --git a/000_HOWTO.md b/000_HOWTO.md
@@ -1,3 +1,5 @@
+# Writing a dynamic library in Crystal, and calling it from C
+
 * Download all files.
 * Build the Crystal part:
 
@@ -11,7 +13,7 @@ crystal build --release --cross-compile --prelude ./no_main library.cr
 * Link the Crystal part into a shared library.  The previous command gives you the line, though we have to modify it a bit:
 
 ```
-gcc foo.o -o libfoo.so -rdynamic -shared -lpcre -lgc -lpthread /usr/lib/crystal/ext/libcrystal.a -levent -lrt -ldl -L/usr/lib -L/usr/local/lib
+gcc library.o -o libfoo.so -rdynamic -shared -lpcre -lgc -lpthread /usr/lib/crystal/ext/libcrystal.a -levent -lrt -ldl -L/usr/lib -L/usr/local/lib
                                  ^ Add this to link into a shared lib
              ^ We want a decent name for the shared lib too.
 ```
@@ -30,4 +32,24 @@ gcc -o program program.c -L$PWD -lfoo
 ./program
 ```
 
+* Verify (Linux only):
+
+Using `ldd program`, we see the dynamic dependencies of our program:
+
+```
+        linux-vdso.so.1 (0x00007ffc56d8c000)
+        libfoo.so (0x00007f80846e9000)         <---- Here it is!
+        libc.so.6 => /usr/lib/libc.so.6 (0x00007f8084343000)
+        libpcre.so.1 => /usr/lib/libpcre.so.1 (0x00007f80840d0000)
+        libgc.so.1 => /usr/lib/libgc.so.1 (0x00007f8083e66000)
+        libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f8083c48000)
+        libevent-2.1.so.6 => /usr/lib/libevent-2.1.so.6 (0x00007f80839f2000)
+        librt.so.1 => /usr/lib/librt.so.1 (0x00007f80837ea000)
+        libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f80835e6000)
+        libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f80833cf000)
+        /lib64/ld-linux-x86-64.so.2 (0x00007f8084909000)
+        libatomic_ops.so.1 => /usr/lib/libatomic_ops.so.1 (0x00007f80831cc000)
+        libcrypto.so.1.1 => /usr/lib/libcrypto.so.1.1 (0x00007f8082d4c000)
+```
 
+## Enjoy!
diff --git a/000_HOWTO.md b/000_HOWTO.md
@@ -0,0 +1,33 @@
+* Download all files.
+* Build the Crystal part:
+
+```
+crystal build --release --cross-compile --prelude ./no_main library.cr
+              ^ You can leave this out
+                        ^ We want to link ourselves!
+                                        ^ Use our custom prelude!
+```
+
+* Link the Crystal part into a shared library.  The previous command gives you the line, though we have to modify it a bit:
+
+```
+gcc foo.o -o libfoo.so -rdynamic -shared -lpcre -lgc -lpthread /usr/lib/crystal/ext/libcrystal.a -levent -lrt -ldl -L/usr/lib -L/usr/local/lib
+                                 ^ Add this to link into a shared lib
+             ^ We want a decent name for the shared lib too.
+```
+
+* Build and link the C program:
+
+```
+gcc -o program program.c -L$PWD -lfoo
+                         ^ We stored our lib right 'here'
+                                ^ And we want to link to it
+```
+
+* Run the program:
+
+```
+./program
+```
+
+
diff --git a/library.cr b/library.cr
@@ -0,0 +1,4 @@
+# The function we will call from C.  Add more `fun`s as you see fit.
+fun hello_crystal : Void
+  puts "Hello from Crystal!"
+end
diff --git a/no_main.cr b/no_main.cr
@@ -0,0 +1,79 @@
+# Copied from my prelude.cr.  Only commented line 50 in this file as change.
+
+# Entries to this file should only be ordered if macros are involved -
+# macros need to be defined before they are used.
+# A first compiler pass gathers all classes and methods, removing the
+# requirement to place these in load order.
+#
+# When adding new files, use alpha-sort when possible. Make sure
+# to also add them to `docs_main.cr` if their content need to
+# appear in the API docs.
+
+# This list requires ordered statements
+require "lib_c"
+require "macros"
+require "object"
+require "comparable"
+require "exception"
+require "iterable"
+require "iterator"
+require "indexable"
+require "string"
+
+# Alpha-sorted list
+require "array"
+require "atomic"
+require "bool"
+require "box"
+require "char"
+require "char/reader"
+require "class"
+require "concurrent"
+require "deque"
+require "dir"
+require "enum"
+require "enumerable"
+require "env"
+require "errno"
+require "ext"
+require "file"
+require "float"
+require "gc"
+# require "gc/null"
+require "gc/boehm"
+require "hash"
+require "iconv"
+require "int"
+require "intrinsics"
+require "io"
+require "kernel"
+# require "main" #### We don't want this!
+require "math/math"
+require "mutex"
+require "named_tuple"
+require "nil"
+require "number"
+require "pointer"
+require "pretty_print"
+require "primitives"
+require "proc"
+require "process"
+require "raise"
+require "random"
+require "range"
+require "reference"
+require "reflect"
+require "regex"
+require "set"
+require "signal"
+require "slice"
+require "static_array"
+require "struct"
+require "symbol"
+require "system"
+require "thread"
+require "time"
+require "tuple"
+require "unicode"
+require "union"
+require "value"
diff --git a/program.c b/program.c
@@ -0,0 +1,5 @@
+void hello_crystal(); // Manually declare Crystal `fun`
+
+int main() {
+  hello_crystal(); // Call to Crystal
+}