Use return in place of exit() in README and samples

Only those places in the README where an error is explicitly found in the
main function have been updated.  Other uses of exit are left untouched as
there is not enough context to know if return will work in that location.

Signed-off-by: Sean Robinson <sean.robinson@scottsdalecc.edu>

README.md

@@ -99,7 +99,7 @@ int main(int argc, char *argv[]) {
   catch (const std::runtime_error& err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   auto input = program.get<int>("square");
@@ -781,7 +781,7 @@ int main(int argc, char *argv[]) {
   catch (const std::runtime_error& err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   // Use arguments
@@ -908,7 +908,7 @@ int main(int argc, char *argv[]) {
   catch (const std::runtime_error& err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program.is_used("+f")) {
@@ -956,7 +956,7 @@ int main(int argc, char *argv[]) {
   catch (const std::runtime_error& err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program.is_used("--foo")) {
@@ -1104,7 +1104,7 @@ int main(int argc, char *argv[]) {
   catch (const std::runtime_error& err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program.is_used("--foo")) {

samples/compound_arguments.cpp

@@ -19,7 +19,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   auto a = program.get<bool>("-a");               // true

samples/custom_assignment_characters.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program.is_used("--foo")) {

samples/custom_prefix_characters.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program.is_used("+f")) {

samples/gathering_remaining_arguments.cpp

@@ -12,7 +12,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   try {

samples/is_used.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   auto color = program.get<std::string>("--color"); // "orange"

samples/joining_repeated_optional_arguments.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   auto colors = program.get<std::vector<std::string>>(

samples/list_of_arguments.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   auto files = program.get<std::vector<std::string>>(

samples/negative_numbers.cpp

@@ -17,7 +17,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program.is_used("integer")) {

samples/optional_flag_argument.cpp

@@ -15,7 +15,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   if (program["--verbose"] == true) {

samples/positional_argument.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   int input = program.get<int>("square");

samples/required_optional_argument.cpp

@@ -14,7 +14,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   std::cout << "Output written to " << program.get("-o") << "\n";

samples/subcommands.cpp

@@ -60,7 +60,7 @@ int main(int argc, char *argv[]) {
   } catch (const std::runtime_error &err) {
     std::cerr << err.what() << std::endl;
     std::cerr << program;
-    std::exit(1);
+    return 1;
   }
 
   // Use arguments