commit d3a3ab40b7cfe3aa5adbcbc7895ec48d39dc89c1
Author:     Albrecht Schlosser <albrechts.fltk@online.de>
AuthorDate: Mon Mar 18 22:29:50 2024 +0100
Commit:     Albrecht Schlosser <albrechts.fltk@online.de>
CommitDate: Mon Mar 18 22:29:50 2024 +0100

    Replace setenv() with putenv() on old systems (+937)
    
    Add system check for setenv() function in configure and CMake.

 CMake/resources.cmake                    |  2 ++
 configh.cmake.in                         |  8 ++++++++
 configh.in                               |  8 ++++++++
 configure.ac                             |  3 +++
 src/drivers/X11/Fl_X11_Screen_Driver.cxx | 23 ++++++++++++++++++++---
 5 files changed, 41 insertions(+), 3 deletions(-)

diff --git CMake/resources.cmake CMake/resources.cmake
index 50d630d..4cc2d3b 100644
--- CMake/resources.cmake
+++ CMake/resources.cmake
@@ -204,6 +204,8 @@ CHECK_FUNCTION_EXISTS (strlcat                  HAVE_STRLCAT)
 CHECK_FUNCTION_EXISTS (strlcpy                  HAVE_STRLCPY)
 CHECK_FUNCTION_EXISTS (vsnprintf                HAVE_VSNPRINTF)
 
+check_function_exists(setenv                    HAVE_SETENV)
+
 if(HAVE_SCANDIR AND NOT HAVE_SCANDIR_POSIX)
    set(MSG "POSIX compatible scandir")
    message(STATUS "Looking for ${MSG}")
diff --git configh.cmake.in configh.cmake.in
index 0dc1b9f..982e9f8 100644
--- configh.cmake.in
+++ configh.cmake.in
@@ -241,6 +241,14 @@
 #cmakedefine01 USE_POLL
 
 /*
+ * HAVE_SETENV:
+ *
+ * Whether or not POSIX setenv() is available from stdlib.h.
+ */
+
+#cmakedefine01 HAVE_SETENV
+
+/*
  * Do we have various image libraries?
  */
 
diff --git configh.in configh.in
index 54ade6c..54ddf96 100644
--- configh.in
+++ configh.in
@@ -240,6 +240,14 @@
 #define USE_POLL 0
 
 /*
+ * HAVE_SETENV:
+ *
+ * Whether or not POSIX setenv() is available from stdlib.h.
+ */
+
+#define HAVE_SETENV 0
+
+/*
  * Do we have various image libraries?
  */
 
diff --git configure.ac configure.ac
index 6b64110..e519f84 100644
--- configure.ac
+++ configure.ac
@@ -620,6 +620,9 @@ AC_CHECK_FUNCS([strcasecmp strlcat strlcpy])
 AC_CHECK_HEADERS([locale.h])
 AC_CHECK_FUNCS([localeconv])
 
+dnl HP-UX 11.11 does not provide setenv()
+AC_CHECK_FUNCS([setenv])
+
 
 dnl FLTK library uses math library functions...
 AC_SEARCH_LIBS([pow], [m])
diff --git src/drivers/X11/Fl_X11_Screen_Driver.cxx src/drivers/X11/Fl_X11_Screen_Driver.cxx
index 7987536..8dc79fc 100644
--- src/drivers/X11/Fl_X11_Screen_Driver.cxx
+++ src/drivers/X11/Fl_X11_Screen_Driver.cxx
@@ -75,9 +75,26 @@ Fl_X11_Screen_Driver::Fl_X11_Screen_Driver() : Fl_Unix_Screen_Driver() {
   key_table_size = 0;
 }
 
-void Fl_X11_Screen_Driver::display(const char *d)
-{
-  if (d) setenv("DISPLAY", d, 1);
+void Fl_X11_Screen_Driver::display(const char *d) {
+  if (!d) return;
+  // Issue #937:
+  // setenv() is available since POSIX.1-2001
+  // https://pubs.opengroup.org/onlinepubs/009604499/functions/setenv.html
+#if HAVE_SETENV
+  setenv("DISPLAY", d, 1);
+#else  // HAVE_SETENV
+  // Use putenv() for old systems (similar to FLTK 1.3)
+  static char e[1024];
+  strcpy(e, "DISPLAY=");
+  strlcat(e, d, sizeof(e));
+  for (char *c = e + 8; *c != ':'; c++) {
+    if (!*c) {
+      strlcat(e,":0.0",sizeof(e));
+      break;
+    }
+  }
+  putenv(e);
+#endif  // HAVE_SETENV
 }
 
 void fl_x11_use_display(Display *d) {