code review 148370043: os, syscall: add Unsetenv

src/runtime/env_posix.go

 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris windows
 
 package runtime
 
 import "unsafe"
 
@@ skipping 14 matching lines @@
                 gothrow("getenv before env init")
         }
         for _, s := range environ() {
                 if len(s) > len(key) && s[len(key)] == '=' && s[:len(key)] == key {
                         return s[len(key)+1:]
                 }
         }
         return ""
 }
 
-var _cgo_setenv uintptr // pointer to C function
+var _cgo_setenv uintptr   // pointer to C function
+var _cgo_unsetenv uintptr // pointer to C function
 
 // Update the C environment if cgo is loaded.
 // Called from syscall.Setenv.
 func syscall_setenv_c(k string, v string) {
         if _cgo_setenv == 0 {
                 return
         }
         arg := [2]unsafe.Pointer{cstring(k), cstring(v)}
         asmcgocall(unsafe.Pointer(_cgo_setenv), unsafe.Pointer(&arg))
 }
 
+// Update the C environment if cgo is loaded.
+// Called from syscall.unsetenv.
+func syscall_unsetenv_c(k string) {
+        if _cgo_unsetenv == 0 {
+                return
+        }
+        arg := [1]unsafe.Pointer{cstring(k)}
+        asmcgocall(unsafe.Pointer(_cgo_unsetenv), unsafe.Pointer(&arg))
+}
+
 func cstring(s string) unsafe.Pointer {
         p := make([]byte, len(s)+1)
         sp := (*_string)(unsafe.Pointer(&s))
         memmove(unsafe.Pointer(&p[0]), unsafe.Pointer(sp.str), uintptr(len(s)))
         return unsafe.Pointer(&p[0])
 }