MSVC error C2026: string too big

[gibki]

I have a huge enum (6000+ options) in my cdef. The generated C code for the array of _cffi_enum_s, field enumerators thus contains a humongous string which trips MSVC.

Huge generated strings need to be split. As a workaround I resorted to having typedef ... MyEnum; in the cdef, but now I don't have MyEnum's fields on my imported lib object.

[arigo]

@nitzmahone Here is a patch to fix the problem. As usual, I'm not used to github enough to make a pull request without spending a lot more time than I spent on this patch.

commit 020651d929f8f28b5e4a264c91f5302908295868
Author: Armin Rigo <armin.rigo@gmail.com>
Date:   Fri May 2 17:53:58 2025 +0200

    split a big generated C string into multiple pieces, for MSVC

diff --git a/src/cffi/recompiler.py b/src/cffi/recompiler.py
index 7734a348..3183a4e7 100644
--- a/src/cffi/recompiler.py
+++ b/src/cffi/recompiler.py
@@ -93,9 +93,18 @@ class EnumExpr:
         self.allenums = allenums
 
     def as_c_expr(self):
-        return ('  { "%s", %d, _cffi_prim_int(%s, %s),\n'
-                '    "%s" },' % (self.name, self.type_index,
-                                 self.size, self.signed, self.allenums))
+        lines = ['  { "%s", %d, _cffi_prim_int(%s, %s),' % (self.name, self.type_index,
+                                                            self.size, self.signed,)]
+        pending = 0
+        while len(self.allenums) > pending + 110:
+            j = self.allenums.find(',', pending + 100)
+            if j < 0:
+                break
+            j += 1
+            lines.append('    "%s"' % (self.allenums[pending:j],))
+            pending = j
+        lines.append('    "%s" },' % (self.allenums[pending:],))
+        return '\n'.join(lines)
 
     def as_python_expr(self):
         prim_index = {
diff --git a/testing/cffi1/test_recompiler.py b/testing/cffi1/test_recompiler.py
index f36512a3..fa7fec22 100644
--- a/testing/cffi1/test_recompiler.py
+++ b/testing/cffi1/test_recompiler.py
@@ -2575,3 +2575,22 @@ def test_convert_api_mode_builtin_function_to_cdata():
     my_array_2 = ffi.new("void *[]", [lib.add1, lib.add2])
     assert ffi.cast("struct s(*)(struct s)", my_array_2[1])(s).x == 302
     assert ffi.typeof(lib.add1) == ffi.typeof("struct s(*)(struct s)")
+
+def test_large_enum():
+    ffi = FFI()
+    biglist = ['nn%d' % i for i in range(6000)]
+    ffi.cdef(
+        """enum foo_s { %s };""" % ','.join(biglist))
+    lib = verify(ffi, "test_large_enum", """
+        enum foo_s { %s };""" % ','.join(biglist))
+    assert lib.nn0 == 0
+    assert lib.nn1234 == 1234
+    assert lib.nn5999 == 5999
+    e = ffi.typeof("enum foo_s")
+    elements = {}
+    relements = {}
+    for i in range(6000):
+        elements[i] = biglist[i]
+        relements[biglist[i]] = i
+    assert e.elements == elements
+    assert e.relements == relements

[mattip]

Applied the patch in #167