lib: add strtol into utility library

The utility library is for functions which are shared in commands,
but that does not belong to libproc-ng.  The first function is a
wrapper for strtol that performs error checking, and exists if such
happen.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

lib/strutils.c

@@ -0,0 +1,34 @@
+#include <stdlib.h>
+
+#include "c.h"
+#include "strutils.h"
+
+/*
+ * same as strtol(3) but exit on failure instead of returning crap
+ */
+long strtol_or_err(const char *str, const char *errmesg)
+{
+	long num;
+	char *end = NULL;
+
+	if (str == NULL || *str == '\0')
+		goto err;
+	errno = 0;
+	num = strtol(str, &end, 10);
+	if (errno || str == end || (end && *end))
+		goto err;
+
+	return num;
+ err:
+	if (errno)
+		err(EXIT_FAILURE, "%s: '%s'", errmesg, str);
+	else
+		errx(EXIT_FAILURE, "%s: '%s'", errmesg, str);
+}
+
+#ifdef TEST_PROGRAM
+int main(int argc, char *argv[])
+{
+	return EXIT_FAILURE;
+}
+#endif				/* TEST_PROGRAM */