2 files changed, 12 insertions(+), 1 deletions(-)

M lisp/ob-C.el
M testing/lisp/test-ob-C.el

@@ 339,7 339,7 @@ FORMAT can be either a format string or a function which is called with VAL."
 	 (type
 	  (pcase basetype
 	    (`integerp '("int" "%d"))
-	    (`floatp '("double" "%f"))
+	    (`floatp '("double" "%s")) ;; %f rounds, use %s to print the float literally
 	    (`stringp
 	     (list
 	      (if (eq org-babel-c-variant 'd) "string" "const char*")

@@ 95,6 95,17 @@
 		      (org-babel-next-src-block 10)
 		      (should (= 42 (org-babel-execute-src-block))))))
 
+(ert-deftest ob-C/float-var ()
+  "Test that floats are passed without unnecessary rounding."
+  (if (executable-find org-babel-C++-compiler)
+      (org-test-with-temp-text 
+"#+source: float_var
+#+begin_src cpp :var x=1.123456789012345678 :includes \"<iostream>\" :results silent
+double y = 1.123456789012345678;
+std::cout << (x == y);
+#+end_src"
+(should (= 1 (org-babel-execute-src-block))))))
+
 (ert-deftest ob-C/table ()
   "Test of a table output"
   (if (executable-find org-babel-C++-compiler)