问题描述：

method_cfg["input_method"][0].asString()

报错误：

test1.cpp:40:46: error: ambiguous overload for ‘operator[]’ in ‘method_cfg.Json::Value::operator[](((const char*)"input_method"))[0]’

test1.cpp:40:46: note: candidates are:

/usr/include/json/value.h:277:14: note: Json::Value& Json::Value::operator[](Json::Value::UInt)

/usr/include/json/value.h:281:20: note: const Json::Value& Json::Value::operator[](Json::Value::UInt) const

/usr/include/json/value.h:294:14: note: Json::Value& Json::Value::operator[](const char*)

/usr/include/json/value.h:296:20: note: const Json::Value& Json::Value::operator[](const char*) const

/usr/include/json/value.h:298:14: note: Json::Value& Json::Value::operator[](const string&)

/usr/include/json/value.h:300:20: note: const Json::Value& Json::Value::operator[](const string&) const

原因和解答：

原因很简单，当是常量值0的时候，无法确定把它当作是 UINT 还是const char*,string来处理。

使用method_cfg["input_method"][0U].asString()或者使用变量 int n=0来代替