man: use external .c files for three examples

This way it's much easier to test that the code compiles without issues.
It's also easier to edit the code.

Indentation in one of the examples is reduced to two spaces. This is what we
use in man pages to make them fit on screen better.

1 files changed, 21 insertions, 0 deletions

diff --git a/man/journal-enumerate-fields.c b/man/journal-enumerate-fields.c
new file mode 100644
index 0000000000..8a35785440
--- /dev/null
+++ b/man/journal-enumerate-fields.c
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: CC0-1.0 */
+
+#include <stdio.h>
+#include <string.h>
+#include <systemd/sd-journal.h>
+
+int main(int argc, char *argv[]) {
+  sd_journal *j;
+  const char *field;
+  int r;
+
+  r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
+  if (r < 0) {
+    fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
+    return 1;
+  }
+  SD_JOURNAL_FOREACH_FIELD(j, field)
+    printf("%s\n", field);
+  sd_journal_close(j);
+  return 0;
+}