all: add format strings

README.md

@@ -14,12 +14,14 @@ If you still want to, `make install` will install this utility to
 ## Usage
 
 ```
-Usage: bin/n [options]
+Usage: n [options]
 Options:
   -h HOST, --host=HOST        NTP server to use
              defaults to 'europe.pool.ntp.org'
   -p PORT, --port=PORT        NTP server port to use (must be numerical)
              defaults to '123'
+  -f FORMAT, --format=FORMAT  Date format string (passed to strftime)
+             defaults to standard of ctime
   --help                      Display this message and exit
 ```
 

main.c

@@ -45,22 +45,36 @@ typedef struct {
 typedef struct {
   const char* host;
   int port;
+  const char* format;
 } ntp_info;
 
-ntp_info NDEFAULT = {.host="europe.pool.ntp.org", .port = 123};
+ntp_info NDEFAULT = {.host="europe.pool.ntp.org", .port = 123, .format = NULL};
 
-void err(char* msg) {
+char* nstrftime(const char* fmt, const struct tm* t) {
+  int size = 40;
+  char* res = malloc(size);
+  int n;
+  do {
+    n = strftime(res, size-1, fmt, t);
+    size *= 2;
+  } while (!n);
+  return res;
+}
+
+void err(const char* msg) {
   fprintf(stderr, "Error %s.\n", msg);
   exit(1);
 }
 
-void usage(char* program, int code) {
+void usage(const char* program, int code) {
   fprintf(stderr, "Usage: %s [options]\n", program);
   fputs("Options:\n", stderr);
   fputs("  -h HOST, --host=HOST        NTP server to use\n", stderr);
   fputs("             defaults to 'europe.pool.ntp.org'\n", stderr);
   fputs("  -p PORT, --port=PORT        NTP server port to use (must be numerical)\n", stderr);
   fputs("             defaults to '123'\n", stderr);
+  fputs("  -f FORMAT, --format=FORMAT  Date format string (passed to strftime)\n", stderr);
+  fputs("             defaults to standard of ctime\n", stderr);
   fputs("  --help                      Display this message and exit\n", stderr);
   exit(code);
 }
@@ -71,12 +85,14 @@ ntp_info args(int argc, char** argv) {
   static struct option long_options[] = {
     {"host", required_argument, 0, 'h'},
     {"port", required_argument, 0, 'p'},
+    {"format", required_argument, 0, 'f'},
     {"help", no_argument, 0, 'u'},
     {NULL, 0, NULL, 0}
   };
-  while ((c = getopt_long(argc, argv, "t:a:", long_options, 0)) != -1) {
+  while ((c = getopt_long(argc, argv, "t:a:f:", long_options, 0)) != -1) {
     switch (c) {
       case 'h': res.host = optarg; break;
+      case 'f': res.format = optarg; break;
       case 'p': {
         char* end;
         res.port = strtol(optarg, &end, 10);
@@ -123,7 +139,13 @@ int main(int argc, char** argv) {
 
   time_t tm = n.ttms - EPOCH;
 
+  if (!i.format) {
     fputs(ctime(&tm), stdout);
+  } else {
+    char* fmt = nstrftime(i.format, localtime(&tm));
+    puts(fmt);
+    free(fmt);
+  }
 
   return 0;
 }