feat: show usage on unknown arg (#767)

Author: stduhpf

examples/cli/main.cpp

@@ -297,10 +297,12 @@ bool parse_options(int argc, const char** argv, ArgOptions& options) {
     bool invalid_arg = false;
     std::string arg;
     for (int i = 1; i < argc; i++) {
+        bool found_arg = false;
         arg = argv[i];
 
         for (auto& option : options.string_options) {
             if ((option.short_name.size() > 0 && arg == option.short_name) || (option.long_name.size() > 0 && arg == option.long_name)) {
+                found_arg = true;
                 if (++i >= argc) {
                     invalid_arg = true;
                     break;
@@ -314,6 +316,7 @@ bool parse_options(int argc, const char** argv, ArgOptions& options) {
 
         for (auto& option : options.int_options) {
             if ((option.short_name.size() > 0 && arg == option.short_name) || (option.long_name.size() > 0 && arg == option.long_name)) {
+                found_arg = true;
                 if (++i >= argc) {
                     invalid_arg = true;
                     break;
@@ -327,6 +330,7 @@ bool parse_options(int argc, const char** argv, ArgOptions& options) {
 
         for (auto& option : options.float_options) {
             if ((option.short_name.size() > 0 && arg == option.short_name) || (option.long_name.size() > 0 && arg == option.long_name)) {
+                found_arg = true;
                 if (++i >= argc) {
                     invalid_arg = true;
                     break;
@@ -340,6 +344,7 @@ bool parse_options(int argc, const char** argv, ArgOptions& options) {
 
         for (auto& option : options.bool_options) {
             if ((option.short_name.size() > 0 && arg == option.short_name) || (option.long_name.size() > 0 && arg == option.long_name)) {
+                found_arg = true;
                 if (option.keep_true) {
                     *option.target = true;
                 } else {
@@ -353,6 +358,7 @@ bool parse_options(int argc, const char** argv, ArgOptions& options) {
 
         for (auto& option : options.manual_options) {
             if ((option.short_name.size() > 0 && arg == option.short_name) || (option.long_name.size() > 0 && arg == option.long_name)) {
+                found_arg = true;
                 int ret = option.cb(argc, argv, i);
                 if (ret < 0) {
                     invalid_arg = true;
@@ -364,6 +370,10 @@ bool parse_options(int argc, const char** argv, ArgOptions& options) {
         if (invalid_arg) {
             break;
         }
+        if (!found_arg) {
+            fprintf(stderr, "error: unknown argument: %s\n", arg.c_str());    
+            return false;
+        }
     }
     if (invalid_arg) {
         fprintf(stderr, "error: invalid parameter for argument: %s\n", arg.c_str());