implement and use a platform neutral abstraction of unsetenv(3)

doc/src/Developer_platform.rst

@@ -118,6 +118,9 @@ Environment variable functions
 .. doxygenfunction:: putenv
    :project: progguide
 
+.. doxygenfunction:: unsetenv
+   :project: progguide
+
 .. doxygenfunction:: list_pathenv
    :project: progguide
 

src/platform.cpp

@@ -446,11 +446,11 @@ int platform::putenv(const std::string &vardef)
 
   auto found = vardef.find_first_of('=');
 #ifdef _WIN32
-  // must assign a value to variable with _putenv()
+  // must assign a value to variable with _putenv_s()
   if (found == std::string::npos)
-    return _putenv(utils::strdup(vardef + "=1"));
+    return _putenv_s(vardef.c_str(), "1");
   else
-    return _putenv(utils::strdup(vardef));
+    return _putenv_s(vardef.substr(0, found).c_str(), vardef.substr(found+1).c_str());
 #else
   if (found == std::string::npos)
     return setenv(vardef.c_str(), "", 1);
@@ -460,6 +460,24 @@ int platform::putenv(const std::string &vardef)
   return -1;
 }
 
+/* ----------------------------------------------------------------------
+   unset environment variable
+------------------------------------------------------------------------- */
+
+int platform::unsetenv(const std::string &variable)
+{
+  if (variable.size() == 0) return -1;
+#ifdef _WIN32
+  // emulate POSIX semantics by returning -1 on trying to unset non-existing variable
+  const char *ptr = getenv(variable.c_str());
+  if (!ptr) return -1;
+  // empty _putenv_s() definition deletes variable
+  return _putenv_s(variable.c_str(),"");
+#else
+  return ::unsetenv(variable.c_str());
+#endif
+}
+
 /* ----------------------------------------------------------------------
    split a "path" environment variable into a list
 ------------------------------------------------------------------------- */

src/platform.h

@@ -125,6 +125,13 @@ namespace platform {
 
   int putenv(const std::string &vardef);
 
+  /*! Delete variable from the environment
+   *
+   * \param  variable  variable name
+   * \return -1 if failure otherwise 0 */
+
+  int unsetenv(const std::string &variable);
+
   /*! Get list of entries in a path environment variable
    *
    * This provides a list of strings of the entries in an environment

unittest/cplusplus/test_lammps_class.cpp

@@ -363,11 +363,7 @@ TEST(LAMMPS_init, NoOpenMP)
     FILE *fp = fopen("in.lammps_class_noomp", "w");
     fputs("\n", fp);
     fclose(fp);
-#if defined(__WIN32)
-    _putenv("OMP_NUM_THREADS");
-#else
-    unsetenv("OMP_NUM_THREADS");
-#endif
+    platform::unsetenv("OMP_NUM_THREADS");
 
     const char *args[] = {"LAMMPS_init", "-in", "in.lammps_class_noomp", "-log", "none", "-nocite"};
     char **argv        = (char **)args;

unittest/utils/test_platform.cpp

@@ -37,7 +37,7 @@ TEST(Platform, clock)
     ASSERT_GT(ct_used, 1e-4);
 }
 
-TEST(Platform, putenv)
+TEST(Platform, putenv_unsetenv)
 {
     const char *var = getenv("UNITTEST_VAR1");
     ASSERT_EQ(var, nullptr);
@@ -65,6 +65,14 @@ TEST(Platform, putenv)
     ASSERT_THAT(var, StrEq("one=two"));
 
     ASSERT_EQ(platform::putenv(""), -1);
+
+    ASSERT_EQ(platform::unsetenv(""), -1);
+    ASSERT_EQ(platform::unsetenv("UNITTEST_VAR3=two"), -1);
+    var    = getenv("UNITTEST_VAR1");
+    ASSERT_NE(var, nullptr);
+    ASSERT_EQ(platform::unsetenv("UNITTEST_VAR1"), 0);
+    var    = getenv("UNITTEST_VAR1");
+    ASSERT_EQ(var, nullptr);
 }
 
 TEST(Platform, list_pathenv)