1 files changed, 57 insertions, 0 deletions
diff --git a/analyze-utf8.c b/analyze-utf8.c
new file mode 100644
index 0000000..8e8f881
--- /dev/null
+++ b/analyze-utf8.c
@@ -0,0 +1,57 @@
+#include "mbstrings.h"
+#include <uchar.h>
+#include <stdio.h>
+#include <locale.h>
+
+int main(void) {
+  // Make sure to have the platform's mb encoding on input.
+  setlocale(LC_CTYPE, "");
+  // Holds the state of input/output buffering.
+  mbstate_t st = { };
+  // collects the input mb sequence
+  char ib[23];
+  // collects the current UTF-8 mb sequence
+  char8_t ob[5] = { };
+  // the number of input characters for the current code point
+  size_t in = 0;
+  while (fgets(ib, sizeof(ib), stdin)) {
+    // Run through the current line. The last character is
+    // always reserved for the string terminator.
+    for (char* p = ib; (p-ib) < sizeof(ib)-1;) {
+      size_t const n = sizeof(ib)-1-(p-ib);
+      size_t const r = mbrtoc8(ob, p, n, &st);
+      switch (r) {       // Handle the special cases.
+      case mbincomplete: p += n; in += n;    continue;
+      case 0: case mbstored: case mbinvalid: goto INVAL;
+      }
+      p += r; in += r;
+      char8_t* cont = ob+1;  // first character is already stored
+      while (mbrtoc8(cont, "", 1, &st) == mbstored) {
+        cont++;
+      }
+      // Now we have the whole UTF-8. Analyze the result.
+      printf("%s", ((cont-ob) == 1) ? "ASCII\t" : "UTF-8\t");
+      for (char8_t* o = ob; o < cont; ++o) {
+        printf("|%02hhx", *o);
+      }
+      // fgets stopped at an end of a line
+      if (*ob == u8'\n') {
+        puts("|\t~ eol");
+        in = 0;
+        break;
+      } else if (in == (cont-ob)) {
+        printf("|\t~ '%s'\n", ob);
+      } else {
+        printf("|\t%zu→%tu\n", in, (cont-ob));
+      }
+      in = 0;
+    }
+    if (*ob != u8'\n') {
+      fputs("incomplete line\n", stderr);
+    }
+  }
+  return EXIT_SUCCESS;
+ INVAL:
+  fputs("input error, exiting\n", stderr);
+  return EXIT_FAILURE;
+}