lastcha2udp: fix test for valid port number

Found by: Ferry Huberts <mailings@hupie.com>

atoi() never returns errno set, yet errno was tested for.
strtol() does set errno, and does other checks.

1 files changed, 4 insertions, 2 deletions

diff --git a/gps2udp.c b/gps2udp.c
index 8549a129..bcc5a743 100644
--- a/gps2udp.c
+++ b/gps2udp.c
@@ -138,6 +138,7 @@ static int open_udp(char **hostport)
    {
        char *hostname = NULL;
        char *portname = NULL;
+       char *endptr = '\0';
        int  portnum;
        struct hostent *hp;
 
@@ -151,8 +152,9 @@ static int open_udp(char **hostport)
 	   return (-1);
        }
 
-       portnum = atoi(portname);
-       if (errno != 0) {
+       errno = 0;
+       portnum = strtol(portname, &endptr, 10);
+       if (0 == portnum || '\0' != *endptr || 0 != errno) {
 	   (void)fprintf(stderr, "gps2udp: syntax is [-u hostname:port] [%s] is not a valid port number\n",portname);
 	   return (-1);
        }