https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/exceptions.hpp
这是异常类头文件，当然了在nlohmann/json.hpp中也包含了这些异常类
nlohmannh/josn中的异常类继承了c 的标准异常std::exception ,该异常是所有标准 c 异常的父类,标准异常都在头文件< exception > 中，文末附上exception.hpp头文件的全部代码
先看一个用例省略了部分代码，在try中解析文件内容获取到的结果，储存到json对象中，然后使用dump()函数序列化，当这些字符不是utf-8时,dump()函数抛出异常此时我们对获取到的文件内容进行转换，转换为utf-8继续运行
try
{
json tmp;
//......省略
return tmp.dump();
}
catch(nlohmann::detail::exception& e)
{
log_error("json throw an error:%s, try to fix", e.what());
string strret = "{\"result\":0}";
if (e.id == 316)
{
string strcontent = gbk_to_utf8(text);
return filtertext(strcontent, false);
}
return strret;
}
接着来看看ag真人试玩娱乐官网给出的异常说明 type_error ， id：316
json.exception.type_error.316 | invalid utf-8 byte at index 10: 0x7e | the @ref dump function only works with utf-8 encoded strings; that is, if you assign a `std::string` to a json value, make sure it is utf-8 encoded. |
翻译：dump函数仅适用于utf-8编码的字符串；也就是说，如果为json值分配“std:：string”，请确保它是utf-8编码的
事实上nlohmann/json这个库只支持utf-8编码
梳理一下dump()函数抛出异常的过程:
首先找到json.hpp中的dump函数，
string_t dump(const int indent = -1, const char indent_char = ’ ', const bool ensure_ascii = false, const error_handler_t error_handler = error_handler_t::strict) const
在这个dump()函数中调用了类serializer中的dump()方法，代码如下：
serializer s(detail::output_adapter
s.dump();
而serializer类中的dump()方法多处调用了dump_escaped(*val.m_value.string, ensure_ascii);
接着在dump_escaped函数中调用了json_throw(type_error::create(316, "invalid utf-8 byte at index " std::to_string(i) “: 0x” sn));
这里跟一下宏定义
#define json_throw(exception) throw exception
结合文末的exception.hpp中的type_error异常类声明，一目了然
更多丰富的异常处理认真研读exception.hpp以及json.hpp即可
以下为exceptions.hpp头文件
1 #pragma once
2
3 #include // exception
4 #include // runtime_error
5 #include // to_string
6
7 #include
8
9 namespace nlohmann
10 {
11 namespace detail
12 {
13
14 // exceptions //
15
16
17 /*!
18 @brief general exception of the @ref basic_json class
19
20 this class is an extension of `std::exception` objects with a member @a id for
21 exception ids. it is used as the base class for all exceptions thrown by the
22 @ref basic_json class. this class can hence be used as "wildcard" to catch
23 exceptions.
24
25 subclasses:
26 - @ref parse_error for exceptions indicating a parse error
27 - @ref invalid_iterator for exceptions indicating errors with iterators
28 - @ref type_error for exceptions indicating executing a member function with
29 a wrong type
30 - @ref out_of_range for exceptions indicating access out of the defined range
31 - @ref other_error for exceptions indicating other library errors
32
33 @internal
34 @note to have nothrow-copy-constructible exceptions, we internally use
35 `std::runtime_error` which can cope with arbitrary-length error messages.
36 intermediate strings are built with static functions and then passed to
37 the actual constructor.
38 @endinternal
39
40 @liveexample{the following code shows how arbitrary library exceptions can be
41 caught.,exception}
42
43 @since version 3.0.0
44 */
45 class exception : public std::exception
46 {
47 public:
48 /// returns the explanatory string
49 const char* what() const noexcept override
50 {
51 return m.what();
52 }
53
54 /// the id of the exception
55 const int id;
56
57 protected:
58 exception(int id_, const char* what_arg) : id(id_), m(what_arg) {
}
59
60 static std::string name(const std::string& ename, int id_)
61 {
62 return "[json.exception." ename "." std::to_string(id_) "] ";
63 }
64
65 private:
66 /// an exception object as storage for error messages
67 std::runtime_error m;
68 };
69
70 /*!
71 @brief exception indicating a parse error
72
73 this exception is thrown by the library when a parse error occurs. parse errors
74 can occur during the deserialization of json text, cbor, messagepack, as well
75 as when using json patch.
76
77 member @a byte holds the byte index of the last read character in the input
78 file.
79
80 exceptions have ids 1xx.
81
82 name / id | example message | description
83 ------------------------------ | --------------- | -------------------------
84 json.exception.parse_error.101 | parse error at 2: unexpected end of input; expected string literal | this error indicates a syntax error while deserializing a json text. the error message describes that an unexpected token (character) was encountered, and the member @a byte indicates the error position.
85 json.exception.parse_error.102 | parse error at 14: missing or wrong low surrogate | json uses the `\uxxxx` format to describe unicode characters. code points above above 0xffff are split into two `\uxxxx` entries ("surrogate pairs"). this error indicates that the surrogate pair is incomplete or contains an invalid code point.
86 json.exception.parse_error.103 | parse error: code points above 0x10ffff are invalid | unicode supports code points up to 0x10ffff. code points above 0x10ffff are invalid.
87 json.exception.parse_error.104 | parse error: json patch must be an array of objects | [rfc 6902](https://tools.ietf.org/html/rfc6902) requires a json patch document to be a json document that represents an array of objects.
88 json.exception.parse_error.105 | parse error: operation must have string member 'op' | an operation of a json patch document must contain exactly one "op" member, whose value indicates the operation to perform. its value must be one of "add", "remove", "replace", "move", "copy", or "test"; other values are errors.
89 json.exception.parse_error.106 | parse error: array index '01' must not begin with '0' | an array index in a json pointer ([rfc 6901](https://tools.ietf.org/html/rfc6901)) may be `0` or any number without a leading `0`.
90 json.exception.parse_error.107 | parse error: json pointer must be empty or begin with '/' - was: 'foo' | a json pointer must be a unicode string containing a sequence of zero or more reference tokens, each prefixed by a `/` character.
91 json.exception.parse_error.108 | parse error: escape character '~' must be followed with '0' or '1' | in a json pointer, only `~0` and `~1` are valid escape sequences.
92 json.exception.parse_error.109 | parse error: array index 'one' is not a number | a json pointer array index must be a number.
93 json.exception.parse_error.110 | parse error at 1: cannot read 2 bytes from vector | when parsing cbor or messagepack, the byte vector ends before the complete value has been read.
94 json.exception.parse_error.112 | parse error at 1: error reading cbor; last byte: 0xf8 | not all types of cbor or messagepack are supported. this exception occurs if an unsupported byte was read.
95 json.exception.parse_error.113 | parse error at 2: expected a cbor string; last byte: 0x98 | while parsing a map key, a value that is not a string has been read.
96 json.exception.parse_error.114 | parse error: unsupported bson record type 0x0f | the parsing of the corresponding bson record type is not implemented (yet).
97
98 @note for an input with n bytes, 1 is the index of the first character and n 1
99 is the index of the terminating null byte or the end of file. this also
100 holds true when reading a byte vector (cbor or messagepack).
101
102 @liveexample{the following code shows how a `parse_error` exception can be
103 caught.,parse_error}
104
105 @sa - @ref exception for the base class of the library exceptions
106 @sa - @ref invalid_iterator for exceptions indicating errors with iterators
107 @sa - @ref type_error for exceptions indicating executing a member function with
108 a wrong type
109 @sa - @ref out_of_range for exceptions indicating access out of the defined range
110 @sa - @ref other_error for exceptions indicating other library errors
111
112 @since version 3.0.0
113 */
114 class parse_error : public exception
115 {
116 public:
117 /*!
118 @brief create a parse error exception
119 @param[in] id_ the id of the exception
120 @param[in] pos the position where the error occurred (or with
121 chars_read_total=0 if the position cannot be
122 determined)
123 @param[in] what_arg the explanatory string
124 @return parse_error object
125 */
126 static parse_error create(int id_, const position_t& pos, const std::string& what_arg)
127 {
128 std::string w = exception::name("parse_error", id_) "parse error"
129 position_string(pos) ": " what_arg;
130 return parse_error(id_, pos.chars_read_total, w.c_str());
131 }
132
133 static parse_error create(int id_, std::size_t byte_, const std::string& what_arg)
134 {
135 std::string w = exception::name("parse_error", id_) "parse error"
136 (byte_ != 0 ? (" at byte " std::to_string(byte_)) : "")
137 ": " what_arg;
138 return parse_error(id_, byte_, w.c_str());
139 }
140
141 /*!
142 @brief byte index of the parse error
143
144 the byte index of the last read character in the input file.
145
146 @note for an input with n bytes, 1 is the index of the first character and
147 n 1 is the index of the terminating null byte or the end of file.
148 this also holds true when reading a byte vector (cbor or messagepack).
149 */
150 const std::size_t byte;
151
152 private:
153 parse_error(int id_, std::size_t byte_, const char* what_arg)
154 : exception(id_, what_arg), byte(byte_) {
}
155
156 static std::string position_string(const position_t& pos)
157 {
158 return " at line " std::to_string(pos.lines_read 1)
159 ", column " std::to_string(pos.chars_read_current_line);
160 }
161 };
162
163 /*!
164 @brief exception indicating errors with iterators
165
166 this exception is thrown if iterators passed to a library function do not match
167 the expected semantics.
168
169 exceptions have ids 2xx.
170
171 name / id | example message | description
172 ----------------------------------- | --------------- | -------------------------
173 json.exception.invalid_iterator.201 | iterators are not compatible | the iterators passed to constructor @ref basic_json(inputit first, inputit last) are not compatible, meaning they do not belong to the same container. therefore, the range (@a first, @a last) is invalid.
174 json.exception.invalid_iterator.202 | iterator does not fit current value | in an erase or insert function, the passed iterator @a pos does not belong to the json value for which the function was called. it hence does not define a valid position for the deletion/insertion.
175 json.exception.invalid_iterator.203 | iterators do not fit current value | either iterator passed to function @ref erase(iteratortype first, iteratortype last) does not belong to the json value from which values shall be erased. it hence does not define a valid range to delete values from.
176 json.exception.invalid_iterator.204 | iterators out of range | when an iterator range for a primitive type (number, boolean, or string) is passed to a constructor or an erase function, this range has to be exactly (@ref begin(), @ref end()), because this is the only way the single stored value is expressed. all other ranges are invalid.
177 json.exception.invalid_iterator.205 | iterator out of range | when an iterator for a primitive type (number, boolean, or string) is passed to an erase function, the iterator has to be the @ref begin() iterator, because it is the only way to address the stored value. all other iterators are invalid.
178 json.exception.invalid_iterator.206 | cannot construct with iterators from null | the iterators passed to constructor @ref basic_json(inputit first, inputit last) belong to a json null value and hence to not define a valid range.
179 json.exception.invalid_iterator.207 | cannot use key() for non-object iterators | the key() member function can only be used on iterators belonging to a json object, because other types do not have a concept of a key.
180 json.exception.invalid_iterator.208 | cannot use operator[] for object iterators | the operator[] to specify a concrete offset cannot be used on iterators belonging to a json object, because json objects are unordered.
181 json.exception.invalid_iterator.209 | cannot use offsets with object iterators | the offset operators ( , -, =, -=) cannot be used on iterators belonging to a json object, because json objects are unordered.
182 json.exception.invalid_iterator.210 | iterators do not fit | the iterator range passed to the insert function are not compatible, meaning they do not belong to the same container. therefore, the range (@a first, @a last) is invalid.
183 json.exception.invalid_iterator.211 | passed iterators may not belong to container | the iterator range passed to the insert function must not be a subrange of the container to insert to.
184 json.exception.invalid_iterator.212 | cannot compare iterators of different containers | when two iterators are compared, they must belong to the same container.
185 json.exception.invalid_iterator.213 | cannot compare order of object iterators | the order of object iterators cannot be compared, because json objects are unordered.
186 json.exception.invalid_iterator.214 | cannot get value | cannot get value for iterator: either the iterator belongs to a null value or it is an iterator to a primitive type (number, boolean, or string), but the iterator is different to @ref begin().
187
188 @liveexample{the following code shows how an `invalid_iterator` exception can be
189 caught.,invalid_iterator}
190
191 @sa - @ref exception for the base class of the library exceptions
192 @sa - @ref parse_error for exceptions indicating a parse error
193 @sa - @ref type_error for exceptions indicating executing a member function with
194 a wrong type
195 @sa - @ref out_of_range for exceptions indicating access out of the defined range
196 @sa - @ref other_error for exceptions indicating other library errors
197
198 @since version 3.0.0
199 */
200 class invalid_iterator : public exception
201 {
202 public:
203 static invalid_iterator create(int id_, const std::string& what_arg)
204 {
205 std::string w = exception::name("invalid_iterator", id_) what_arg;
206 return invalid_iterator(id_, w.c_str());
207 }
208
209 private:
210 invalid_iterator(int id_, const char* what_arg)
211 : exception(id_, what_arg) {
}
212 };
213
214 /*!
215 @brief exception indicating executing a member function with a wrong type
216
217 this exception is thrown in case of a type error; that is, a library function is
218 executed on a json value whose type does not match the expected semantics.
219
220 exceptions have ids 3xx.
221
222 name / id | example message | description
223 ----------------------------- | --------------- | -------------------------
224 json.exception.type_error.301 | cannot create object from initializer list | to create an object from an initializer list, the initializer list must consist only of a list of pairs whose first element is a string. when this constraint is violated, an array is created instead.
225 json.exception.type_error.302 | type must be object, but is array | during implicit or explicit value conversion, the json type must be compatible to the target type. for instance, a json string can only be converted into string types, but not into numbers or boolean types.
226 json.exception.type_error.303 | incompatible referencetype for get_ref, actual type is object | to retrieve a reference to a value stored in a @ref basic_json object with @ref get_ref, the type of the reference must match the value type. for instance, for a json array, the @a referencetype must be @ref array_t &.
227 json.exception.type_error.304 | cannot use at() with string | the @ref at() member functions can only be executed for certain json types.
228 json.exception.type_error.305 | cannot use operator[] with string | the @ref operator[] member functions can only be executed for certain json types.
229 json.exception.type_error.306 | cannot use value() with string | the @ref value() member functions can only be executed for certain json types.
230 json.exception.type_error.307 | cannot use erase() with string | the @ref erase() member functions can only be executed for certain json types.
231 json.exception.type_error.308 | cannot use push_back() with string | the @ref push_back() and @ref operator = member functions can only be executed for certain json types.
232 json.exception.type_error.309 | cannot use insert() with | the @ref insert() member functions can only be executed for certain json types.
233 json.exception.type_error.310 | cannot use swap() with number | the @ref swap() member functions can only be executed for certain json types.
234 json.exception.type_error.311 | cannot use emplace_back() with string | the @ref emplace_back() member function can only be executed for certain json types.
235 json.exception.type_error.312 | cannot use update() with string | the @ref update() member functions can only be executed for certain json types.
236 json.exception.type_error.313 | invalid value to unflatten | the @ref unflatten function converts an object whose keys are json pointers back into an arbitrary nested json value. the json pointers must not overlap, because then the resulting value would not be well defined.
237 json.exception.type_error.314 | only objects can be unflattened | the @ref unflatten function only works for an object whose keys are json pointers.
238 json.exception.type_error.315 | values in object must be primitive | the @ref unflatten function only works for an object whose keys are json pointers and whose values are primitive.
239 json.exception.type_error.316 | invalid utf-8 byte at index 10: 0x7e | the @ref dump function only works with utf-8 encoded strings; that is, if you assign a `std::string` to a json value, make sure it is utf-8 encoded. |
240 json.exception.type_error.317 | json value cannot be serialized to requested format | the dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw `true` or `null` json object cannot be serialized to bson) |
241
242 @liveexample{the following code shows how a `type_error` exception can be
243 caught.,type_error}
244
245 @sa - @ref exception for the base class of the library exceptions
246 @sa - @ref parse_error for exceptions indicating a parse error
247 @sa - @ref invalid_iterator for exceptions indicating errors with iterators
248 @sa - @ref out_of_range for exceptions indicating access out of the defined range
249 @sa - @ref other_error for exceptions indicating other library errors
250
251 @since version 3.0.0
252 */
253 class type_error : public exception
254 {
255 public:
256 static type_error create(int id_, const std::string& what_arg)
257 {
258 std::string w = exception::name("type_error", id_) what_arg;
259 return type_error(id_, w.c_str());
260 }
261
262 private:
263 type_error(int id_, const char* what_arg) : exception(id_, what_arg) {
}
264 };
265
266 /*!
267 @brief exception indicating access out of the defined range
268
269 this exception is thrown in case a library function is called on an input
270 parameter that exceeds the expected range, for instance in case of array
271 indices or nonexisting object keys.
272
273 exceptions have ids 4xx.
274
275 name / id | example message | description
276 ------------------------------- | --------------- | -------------------------
277 json.exception.out_of_range.401 | array index 3 is out of range | the provided array index @a i is larger than @a size-1.
278 json.exception.out_of_range.402 | array index '-' (3) is out of range | the special array index `-` in a json pointer never describes a valid element of the array, but the index past the end. that is, it can only be used to add elements at this position, but not to read it.
279 json.exception.out_of_range.403 | key 'foo' not found | the provided key was not found in the json object.
280 json.exception.out_of_range.404 | unresolved reference token 'foo' | a reference token in a json pointer could not be resolved.
281 json.exception.out_of_range.405 | json pointer has no parent | the json patch operations 'remove' and 'add' can not be applied to the root element of the json value.
282 json.exception.out_of_range.406 | number overflow parsing '10e1000' | a parsed number could not be stored as without changing it to nan or inf.
283 json.exception.out_of_range.407 | number overflow serializing '9223372036854775808' | ubjson and bson only support integer numbers up to 9223372036854775807. |
284 json.exception.out_of_range.408 | excessive array size: 8658170730974374167 | the size (following `#`) of an ubjson array or object exceeds the maximal capacity. |
285 json.exception.out_of_range.409 | bson key cannot contain code point u 0000 (at byte 2) | key identifiers to be serialized to bson cannot contain code point u 0000, since the key is stored as zero-terminated c-string |
286
287 @liveexample{the following code shows how an `out_of_range` exception can be
288 caught.,out_of_range}
289
290 @sa - @ref exception for the base class of the library exceptions
291 @sa - @ref parse_error for exceptions indicating a parse error
292 @sa - @ref invalid_iterator for exceptions indicating errors with iterators
293 @sa - @ref type_error for exceptions indicating executing a member function with
294 a wrong type
295 @sa - @ref other_error for exceptions indicating other library errors
296
297 @since version 3.0.0
298 */
299 class out_of_range : public exception
300 {
301 public:
302 static out_of_range create(int id_, const std::string& what_arg)
303 {
304 std::string w = exception::name("out_of_range", id_) what_arg;
305 return out_of_range(id_, w.c_str());
306 }
307
308 private:
309 out_of_range(int id_, const char* what_arg) : exception(id_, what_arg) {
}
310 };
311
312 /*!
313 @brief exception indicating other library errors
314
315 this exception is thrown in case of errors that cannot be classified with the
316 other exception types.
317
318 exceptions have ids 5xx.
319
320 name / id | example message | description
321 ------------------------------ | --------------- | -------------------------
322 json.exception.other_error.501 | unsuccessful: {"op":"test","path":"/baz", "value":"bar"} | a json patch operation 'test' failed. the unsuccessful operation is also printed.
323
324 @sa - @ref exception for the base class of the library exceptions
325 @sa - @ref parse_error for exceptions indicating a parse error
326 @sa - @ref invalid_iterator for exceptions indicating errors with iterators
327 @sa - @ref type_error for exceptions indicating executing a member function with
328 a wrong type
329 @sa - @ref out_of_range for exceptions indicating access out of the defined range
330
331 @liveexample{the following code shows how an `other_error` exception can be
332 caught.,other_error}
333
334 @since version 3.0.0
335 */
336 class other_error : public exception
337 {
338 public:
339 static other_error create(int id_, const std::string& what_arg)
340 {
341 std::string w = exception::name("other_error", id_) what_arg;
342 return other_error(id_, w.c_str());
343 }
344
345 private:
346 other_error(int id_, const char* what_arg) : exception(id_, what_arg) {
}
347 };
348 } // namespace detail
349 } // namespace nlohmann