Modify ncdump to print char-valued variables as utf8.

re: Issue #2916

Currently, ncdump prints char-valued variables as a mix
of ascii and octal characters. The octal format is used
for non-printable ascii character values.

This PR changes this to print the char variable values
as raw binary. This means in practice that utf-8 tags
are properly interpreted and printed as utf-8.

.github/workflows/run_tests_osx.yml

@@ -6,7 +6,7 @@
 
 name: Run macOS-based netCDF Tests
 
-on: [push,pull_request,workflow_dispatch]
+on: [pull_request,workflow_dispatch]
 
 concurrency:  
   group: ${{ github.workflow}}-${{ github.head_ref }}  

.github/workflows/run_tests_ubuntu.yml

@@ -4,7 +4,7 @@
 
 name: Run Ubuntu/Linux netCDF Tests
 
-on: [push, pull_request, workflow_dispatch]
+on: [ pull_request, workflow_dispatch]
 
 concurrency:  
   group: ${{ github.workflow}}-${{ github.head_ref }}  

.github/workflows/run_tests_win_cygwin.yml

@@ -1,6 +1,6 @@
 name: Run Cygwin-based tests
 
-on: [push,pull_request,workflow_dispatch]
+on: [pull_request,workflow_dispatch]
 
 concurrency:  
   group: ${{ github.workflow}}-${{ github.head_ref }}  

.github/workflows/run_tests_win_mingw.yml

@@ -9,7 +9,7 @@ name: Run MSYS2, MinGW64-based Tests (Not Visual Studio)
 env:
   CPPFLAGS: "-D_BSD_SOURCE"
 
-on: [push,pull_request,workflow_dispatch]
+on: [pull_request,workflow_dispatch]
 
 concurrency:  
   group: ${{ github.workflow}}-${{ github.head_ref }}  

ncdump/vardata.c

@@ -20,6 +20,12 @@
 #include "vardata.h"
 #include "netcdf_aux.h"
 
+/* If set, then print char variables as utf-8.
+   If not set, then print non-printable characters as octal.
+   The latter was the default before this change.
+*/
+#define UTF8CHARS
+
 /* maximum len of string needed for one value of a primitive type */
 #define MAX_OUTPUT_LEN 100
 
@@ -340,6 +346,7 @@ pr_tvals(
     sp = vals + len;
     while (len != 0 && *--sp == '\0')
 	len--;
+    /* Walk the sequence of characters and write control characters in escape form. */
     for (iel = 0; iel < len; iel++) {
 	unsigned char uc;
 	switch (uc = (unsigned char)(*vals++ & 0377)) {
@@ -371,10 +378,12 @@ pr_tvals(
 	    printf("\\\"");
 	    break;
 	default:
-	    if (isprint(uc))
-		printf("%c",uc);
-	    else
+#ifdef UTF8CHARS
+	    if (!isprint(uc))
 		printf("\\%.3o",uc);
+	    else
+#endif /*UTF8CHARS*/
+		printf("%c",uc);
 	    break;
 	}
     }