Fix nul char (#324)

* special case for the NUL char -- treat it as if it was an empty string, so that we do not emit NUL terminators in the middle of the output, and the result is consistent across pprintf and snprintf

* commented (new) non-standard tests for %lc

---------

Co-authored-by: Stefano Zanotti <[email protected]>

Author: stefano-zanotti-88

nanoprintf.h

@@ -844,7 +844,7 @@ int npf_vpprintf(npf_putc pc, void *pc_ctx, char const *format, va_list args) {
 
       case NPF_FMT_SPEC_CONV_CHAR:
         *cbuf = (char)va_arg(args, int);
-        cbuf_len = 1;
+        cbuf_len = (*cbuf) ? 1 : 0;
         break;
 
       case NPF_FMT_SPEC_CONV_STRING: {

tests/conformance.cc

@@ -79,14 +79,33 @@ TEST_CASE("conformance to system printf") {
   }
 
   SUBCASE("char") {
-    // every char
+    // every char except the NUL char
     for (int i = CHAR_MIN; i < CHAR_MAX; ++i) {
-        char output[2] = {(char)i, 0};
-        require_conform(output, "%c", i);
+        if(i != '\0') {
+          char output[2] = {(char)i, 0};
+          require_conform(output, "%c", i);
+        }
     }
 
     require_conform("A", "%+c", 'A');
-    require_conform("", "%+c", 0);
+
+    // These should be added to non-standard tests (when we add length-checks to the tests)
+    //require_conform("", "%c", '\0'); // ret 0
+    //require_conform("AB", "A%cB", '\0'); // ret 0
+    //require_conform("", "%+c", '\0'); // ret 0
+#if NANOPRINTF_USE_FIELD_WIDTH_FORMAT_SPECIFIERS == 1
+    //require_conform("A          B", "A%10cB", '\0'); // ret 12
+    //require_conform("AB", "A%.5cB", '\0'); // ret 2
+    //require_conform("     ", "%-5c", '\0'); // ret 5
+    //require_conform("    ", "% 4c", '\0'); // ret 4
+#endif
+    //for (int i = CHAR_MIN; i < CHAR_MAX; ++i) {
+    //  if(i != '\0') {
+    //    char output[2] = {(char)i, 0};
+    //    require_conform(output, "%lc", i);
+    //  }
+    //}
+    // end of non-standard tests
 
 #if NANOPRINTF_USE_FIELD_WIDTH_FORMAT_SPECIFIERS == 1
     // right justify field width