another check; simplified code

v5/proj.c

@@ -1,9 +1,5 @@
 #include "proj_go.h"
 
-int pjnull(PJ *pj) {
-    return pj == 0 ? 0 : 1;
-}
-
 void trans(PJ *pj, PJ_DIRECTION direction, double u1, double v1, double w1, double t1, double *u2, double *v2, double *w2, double *t2) {
     PJ_COORD
 	co1,

v5/proj.go

@@ -9,6 +9,7 @@ import "C"
 
 import (
 	"errors"
+	"fmt"
 	"math"
 	"runtime"
 	"unsafe"
@@ -106,7 +107,7 @@ func (ctx *Context) Create(definition string) (*PJ, error) {
 	cs := C.CString(definition)
 	defer C.free(unsafe.Pointer(cs))
 	pj := C.proj_create(ctx.pj_context, cs)
-	if C.pjnull(pj) == 0 {
+	if pj == nil {
 		errno := C.proj_context_errno(ctx.pj_context)
 		err := C.GoString(C.proj_errno_string(errno))
 		return &PJ{}, errors.New(err)
@@ -249,19 +250,23 @@ func (p *PJ) TransSlice(direction Direction, u1, v1, w1, t1 []float64) (u2, v2,
 
 	st := C.size_t(C.sizeof_double)
 
-	C.proj_trans_generic(
+	count := int(C.proj_trans_generic(
 		p.pj,
 		C.PJ_DIRECTION(direction),
 		up, st, unc,
 		vp, st, vnc,
 		wp, st, wnc,
-		tp, st, tnc)
+		tp, st, tnc))
 
 	e := C.proj_errno(p.pj)
 	if e != 0 {
 		return nil, nil, nil, nil, errors.New(C.GoString(C.proj_errno_string(e)))
 	}
 
+	if count != n {
+		return nil, nil, nil, nil, fmt.Errorf("Got %d coordinates, translated %d coordinates", n, count)
+	}
+
 	u2 = make([]float64, un)
 	for i := 0; i < un; i++ {
 		u2[i] = float64(u[i])

v5/proj_go.h

@@ -4,7 +4,6 @@
 #include <proj.h>
 #include <stdlib.h>
 
-int pjnull(PJ *pj);
 void trans(PJ *pj, PJ_DIRECTION direction, double u1, double v1, double w1, double t1, double *u2, double *v2, double *w2, double *t2);
 PJ_COORD uvwt(double u, double v, double w, double t);