Fix bug in DiffInMonths method output error

difference.go

@@ -24,11 +24,27 @@ func (c Carbon) DiffAbsInYears(carbon ...Carbon) int64 {
 // DiffInMonths gets the difference in months.
 // 相差多少月
 func (c Carbon) DiffInMonths(carbon ...Carbon) int64 {
-	start, end := c, c.Now()
+	end := c.Now()
 	if len(carbon) > 0 {
 		end = carbon[len(carbon)-1]
 	}
-	return int64(math.Floor(float64((end.Timestamp() - start.Timestamp()) / (30 * 24 * 3600))))
+	startYear, startMonth, startDay := c.Date()
+	endYear, endMonth, endDay := end.Date()
+
+	diffYear, diffMonth, diffDay := endYear-startYear, endMonth-startMonth, endDay-startDay
+	if diffDay < 0 {
+		diffMonth = diffMonth - 1
+	}
+	if diffYear == 0 && diffMonth == 0 {
+		return int64(0)
+	}
+	if diffYear == 0 && diffMonth != 0 && diffDay != 0 {
+		if int(end.DiffAbsInHours(c)) < c.DaysInMonth()*HoursPerDay {
+			return int64(0)
+		}
+		return int64(diffMonth)
+	}
+	return int64(diffYear*MonthsPerYear + diffMonth)
 }
 
 // DiffAbsInMonths gets the difference in months with absolute value.

difference_test.go

@@ -63,7 +63,7 @@ func TestCarbon_DiffInMonths(t *testing.T) {
 		{"2020-08-05 13:14:15", "2020-09-06 13:14:59", 1},
 		{"2020-12-31 13:14:15", "2021-01-31 13:14:15", 1},
 		{"2020-08-05 13:14:15", "2021-08-28 13:14:59", 12},
-		{"2020-08-05 13:14:15", "2018-08-28 13:14:59", -23},
+		{"2020-08-05 13:14:15", "2018-08-28 13:14:59", -24},
 	}
 
 	for index, test := range tests {
@@ -85,7 +85,7 @@ func TestCarbon_DiffAbsInMonths(t *testing.T) {
 		{"2020-08-05 13:14:15", "2020-07-28 13:14:00", 0},
 		{"2020-12-31 13:14:15", "2021-01-01 13:14:15", 0},
 		{"2020-08-05 13:14:15", "2021-08-28 13:14:59", 12},
-		{"2020-08-05 13:14:15", "2018-08-28 13:14:59", 23},
+		{"2020-08-05 13:14:15", "2018-08-28 13:14:59", 24},
 	}
 
 	for index, test := range tests {