fix snprintf on output size 0

2 files changed, 15 insertions, 2 deletions

diff --git a/src/library.js b/src/library.js
index 06661d59..d0a556be 100644
--- a/src/library.js
+++ b/src/library.js
@@ -3485,11 +3485,11 @@ LibraryManager.library = {
     // http://pubs.opengroup.org/onlinepubs/000095399/functions/printf.html
     var result = __formatString(format, varargs);
     var limit = (n === undefined) ? result.length
-                                  : Math.min(result.length, n - 1);
+                                  : Math.min(result.length, Math.max(n - 1, 0));
     for (var i = 0; i < limit; i++) {
       {{{ makeSetValue('s', 'i', 'result[i]', 'i8') }}};
     }
-    {{{ makeSetValue('s', 'i', '0', 'i8') }}};
+    if (limit < n) {{{ makeSetValue('s', 'i', '0', 'i8') }}};
     return result.length;
   },
   fprintf__deps: ['fwrite', '_formatString'],
diff --git a/tests/runner.py b/tests/runner.py
index f3289e46..deeb5689 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -4318,6 +4318,19 @@ at function.:blag
         '''
       self.do_run(src, re.sub('(^|\n)\s+', '\\1', expected))
 
+    def test_snprintf0(self):
+      src = r'''
+        #include <stdio.h>
+        int main()  {
+          int size = snprintf(NULL, 0, "%s %d %.2f\n", "me and myself", 25, 1.345);
+          char buf[size];
+          snprintf(buf, size, "%s %d %.2f\n", "me and myself", 25, 1.345);
+          printf("%d : %s\n", size, buf);
+          return 0;
+        }
+        '''
+      self.do_run(src, '22 : me and myself 25 1.34\n')
+
     def test_atoX(self):
       if self.emcc_args is None: return self.skip('requires ta2')