Microsoft C/C++ compiler warnings C4000 through C4199
The articles in this section describe Microsoft C/C++ compiler warning messages C4000 through C4199.
Important
The Visual Studio compilers and build tools can report many kinds of errors and warnings. After an error or warning is found, the build tools may make assumptions about code intent and attempt to continue, so that more issues can be reported at the same time. If the tools make the wrong assumption, later errors or warnings may not apply to your project. When you correct issues in your project, always start with the first error or warning that's reported, and rebuild often. One fix may make many subsequent errors go away.
To get help on a particular diagnostic message in Visual Studio, select it in the Output window and press the F1 key. Visual Studio opens the documentation page for that error, if one exists. You can also use the search tool at the top of the page to find articles about specific errors or warnings. Or, browse the list of errors and warnings by tool and type in the table of contents on this page.
Note
Not every Visual Studio error or warning is documented. In many cases, the diagnostic message provides all of the information that's available. If you landed on this page when you used F1 and you think the error or warning message needs additional explanation, let us know. You can use the feedback buttons on this page to raise a documentation issue on GitHub. If you think the error or warning is wrong, or you've found another problem with the toolset, report a product issue on the Developer Community site. You can also send feedback and enter bugs within the IDE. In Visual Studio, go to the menu bar and choose Help > Send Feedback > Report a Problem, or submit a suggestion by using Help > Send Feedback > Send a Suggestion. Some compiler error topics were created that are not emitted by the compiler and now redirect to this page instead.
You may find additional assistance for errors and warnings in Microsoft Learn Q&A forums. Or, search for the error or warning number on the Visual Studio C++ Developer Community site. You can also search Stack Overflow to find solutions.
For links to additional help and community resources, see Visual C++ Help and Community.
Warning messages
| Warning | Message |
|---|---|
| Compiler warning (level 4, no longer emitted) C4001 | nonstandard extension 'single line comment' was used |
| Compiler warning (level 1, Error) C4002 | too many arguments for function-like macro invocation 'identifier' |
| Compiler warning (level 1, Error) C4003 | not enough arguments for function-like macro invocation 'identifier' |
| Compiler warning (level 1) C4005 | 'identifier': macro redefinition |
| Compiler warning (level 1) C4006 | #undef expected an identifier |
| Compiler warning (level 3) C4007 | 'function': must be 'attribute' |
| Compiler warning (level 3) C4008 | 'function': 'attribute' attribute ignored |
| Compiler warning (level 1) C4010 | single-line comment contains line-continuation character |
| Compiler warning (level 3) C4013 | 'function' undefined; assuming extern returning int |
| Compiler warning (level 1) C4015 | 'identifier': type of bit field must be integral |
| Compiler warning (level 3) C4018 | 'expression': signed/unsigned mismatch |
| Compiler warning (level 4) C4019 | empty statement at global scope |
| Compiler warning (level 1) C4020 | 'function': too many actual parameters |
| Compiler warning (level 1) C4022 | 'function': pointer mismatch for actual parameter 'parameter_number' |
| Compiler warning (level 1) C4023 | 'function': based pointer passed to unprototyped function: parameter 'parameter_number' |
| Compiler warning (level 1) C4024 | 'function': different types for formal and actual parameter 'parameter_number' |
| Compiler warning (level 1) C4025 | 'function': based pointer passed to function with variable arguments: parameter 'parameter_number' |
| Compiler warning (level 1) C4026 | function declared with formal parameter list |
| Compiler warning (level 1) C4027 | function declared without formal parameter list |
| Compiler warning (level 1) C4028 | formal parameter parameter_number different from declaration |
| Compiler warning (level 1) C4029 | declared formal parameter list different from definition |
| Compiler warning (level 1) C4030 | first formal parameter list longer than the second list |
| Compiler warning (level 1) C4031 | second formal parameter list longer than the first list |
| Compiler warning (level 4) C4032 | formal parameter parameter_number has different type when promoted |
| Compiler warning (level 1) C4033 | 'function' must return a value |
| Compiler warning (level 1) C4034 | sizeof returns 0 |
| Compiler warning (level 3) C4035 | 'function': no return value |
| Compiler warning (level 1) C4036 | unnamed 'type' as actual parameter |
| Compiler warning (level 1) C4038 | 'modifier': illegal class modifier |
| Compiler warning (level 1) C4041 | compiler limit: terminating browser output |
| Compiler warning (level 1) C4042 | 'identifier': has bad storage class |
| Compiler warning (level 1) C4045 | 'array': array bounds overflow |
| Compiler warning (level 1) C4047 | 'operator': 'identifier1' differs in levels of indirection from 'identifier2' |
| Compiler warning (level 1) C4048 | different array subscripts: 'identifier1' and 'identifier2' |
| Compiler warning (level 1) C4049 | compiler limit: terminating line number emission |
| Compiler warning (level 1) C4051 | type conversion; possible loss of data |
| Compiler warning (level 1 and level 4) C4052 | function declarations different; one contains variable arguments |
| Compiler warning (level 4) C4053 | one void operand for '?:' |
| Compiler warning (level 1) C4055 | 'conversion' : from data pointer 'type1' to function pointer 'type2' |
| Compiler warning (level 2) C4056 | overflow in floating-point constant arithmetic |
| Compiler warning (level 4) C4057 | 'operator': 'identifier1' differs in indirection to slightly different base types from 'identifier2' |
| Compiler warning (level 3, off) C4060 | switch statement contains no 'case' or 'default' labels |
| Compiler warning (level 4, off) C4061 | enumerator 'identifier' in switch of enum 'enumeration' is not explicitly handled by a case label |
| Compiler warning (level 4, off) C4062 | enumerator 'identifier' in switch of enum 'enumeration' is not handled |
| Compiler warning (level 4) C4063 | case 'identifier' is not a valid value for switch of enum 'enumeration' |
| Compiler warning (level 4) C4064 | switch of incomplete enum 'enumeration' |
| Compiler warning (level 3, off) C4065 | switch statement contains 'default' but no 'case' labels |
| Compiler warning (level 3) C4066 | characters beyond first in wide-character constant ignored |
| Compiler warning (level 1) C4067 | unexpected tokens following preprocessor directive - expected a newline |
| Compiler warning (level 1) C4068 | unknown pragma 'identifier' |
| Compiler warning C4069 | long double is the same precision as double |
| Compiler warning (level 3) C4073 | initializers put in library initialization area |
| Compiler warning (level 1) C4074 | initializers put in compiler reserved initialization area |
| Compiler warning (level 1) C4075 | initializers put in unrecognized initialization area |
| Compiler warning (level 1) C4076 | 'type_modifier': can't be used with type 'typename' |
| Compiler warning (level 1) C4077 | unknown check_stack option |
| Compiler warning (level 1) C4079 | unexpected token 'token' |
| Compiler warning (level 1) C4080 | expected identifier for segment name; found 'symbol' |
| Compiler warning (level 1) C4081 | expected 'token1'; found 'token2' |
| Compiler warning (level 1) C4083 | expected 'token'; found identifier 'identifier' |
| Compiler warning (level 1) C4085 | expected pragma parameter to be 'on' or 'off' |
| Compiler warning (level 1) C4086 | expected pragma parameter to be '1', '2', '4', '8', or '16' |
| Compiler warning (level 1) C4087 | 'function': declared with 'void' parameter list |
| Compiler warning (level 1) C4088 | 'function': pointer mismatch in actual parameter 'parameter_number', formal parameter 'parameter_number' |
| Compiler warning (level 1) C4089 | 'function': different types in actual parameter 'parameter_number', formal parameter 'parameter_number' |
| Compiler warning (level 1) C4090 | 'operation': different 'modifier' qualifiers |
| Compiler warning (level 1 and level 2) C4091 | 'keyword': ignored on left of 'type' when no variable is declared |
| Compiler warning (level 4) C4092 | sizeof returns 'unsigned long' |
| Compiler warning (level 2) C4094 | untagged 'token' declared no symbols |
| Compiler warning (level 1) C4096 | 'identifier': interface is not a COM interface; will not be emitted to IDL |
| Compiler warning (level 1) C4097 | expected pragma parameter to be 'restore' or 'off' |
| Compiler warning (level 1) C4098 | 'function': 'void' function returning a value |
| Compiler warning (level 2) C4099 | 'identifier': type name first seen using 'object_type1' now seen using 'object_type2' |
| Compiler warning (level 4) C4100 | 'identifier': unreferenced formal parameter |
| Compiler warning (level 3 and level 4) C4101 | 'identifier': unreferenced local variable |
| Compiler warning (level 3) C4102 | 'label': unreferenced label |
| Compiler warning (level 1) C4103 | alignment changed after including header, may be due to missing #pragma pack(pop) |
| Compiler warning (level 1) C4109 | unexpected identifier 'identifier' |
| Compiler warning (level 1 and level 4) C4112 | #line requires an integer between 1 and 'line_count' |
| Compiler warning (level 1) C4113 | 'identifier1' differs in parameter lists from 'identifier2' |
| Compiler warning (level 1) C4114 | same type qualifier used more than once |
| Compiler warning (level 1 and level 4) C4115 | 'type': named type definition in parentheses |
| Compiler warning (level 1) C4116 | unnamed type definition in parentheses |
| Compiler warning (level 1) C4117 | macro name 'name' is reserved, 'command' ignored |
| Compiler warning (level 1) C4119 | different bases 'base1' and 'base2' specified |
| Compiler warning (level 1) C4120 | based/unbased mismatch |
| Compiler warning (level 4) C4121 | 'symbol': alignment of a member was sensitive to packing |
| Compiler warning (level 1) C4122 | 'function': alloc_text applicable only to functions with C linkage |
| Compiler warning (level 1) C4123 | different base expressions specified |
| Compiler warning (level 1) C4124 | __fastcall with stack checking is inefficient |
| Compiler warning (level 4) C4125 | decimal digit terminates octal escape sequence |
| Compiler warning (level 4) C4127 | conditional expression is constant |
| Compiler warning (level 1) C4129 | 'character': unrecognized character escape sequence |
| Compiler warning (level 4) C4130 | 'operator': logical operation on address of string constant |
| Compiler warning (level 4) C4131 | 'function': uses old-style declarator |
| Compiler warning (level 4) C4132 | 'object': const object should be initialized |
| Compiler warning (level 1 and level 3) C4133 | 'expression': incompatible types - from 'type1' to 'type2' |
| Compiler warning C4137 | 'function': no return value from floating-point function |
| Compiler warning (level 1) C4138 | '*/' found outside of comment |
| Compiler warning (level 1, Error) C4141 | 'modifier': used more than once |
| Compiler warning (level 1) C4142 | 'identifier': benign redefinition of type |
| Compiler warning (level 1) C4143 | pragma 'same_seg' not supported; use __based allocation |
| Compiler warning (level 1) C4144 | 'expression': relational expression as switch expression |
| Compiler warning (level 1) C4145 | 'expression1': relational expression as switch expression; possible confusion with 'expression2' |
| Compiler warning (level 2) C4146 | unary minus operator applied to unsigned type, result still unsigned |
| Compiler warning (level 2) C4150 | deletion of pointer to incomplete type 'type'; no destructor called |
| Compiler warning (level 4) C4152 | nonstandard extension, function/data pointer conversion in expression |
| Compiler warning (level 1) C4153 | function/data pointer conversion in expression |
| Compiler warning (level 1) C4154 | deletion of an array expression; conversion to pointer supplied |
| Compiler warning (level 1) C4155 | deletion of an array expression without using the array form of 'delete' |
| Compiler warning (level 2) C4156 | deletion of an array expression without using the array form of 'delete'; array form substituted |
| Compiler warning (level 1) C4157 | pragma was ignored by C compiler |
| Compiler warning (level 1) C4158 | assuming #pragma pointers_to_members(full_generality, 'inheritance_type') |
| Compiler warning (level 3) C4159 | #pragma 'pragma'(pop,...): has popped previously pushed identifier 'identifier' |
| Compiler warning (level 1) C4160 | #pragma 'pragma'(pop,...): did not find previously pushed identifier 'identifier' |
| Compiler warning (level 3) C4161 | #pragma 'pragma'(pop...): more pops than pushes |
| Compiler warning (level 1) C4162 | 'identifier': no function with C linkage found |
| Compiler warning (level 1) C4163 | 'identifier': not available as an intrinsic function |
| Compiler warning (level 1) C4164 | 'function': intrinsic function not declared |
| Compiler warning (level 3, off) C4165 | 'HRESULT' is being converted to 'bool'; are you sure this is what you want? |
| Compiler warning (level 1) C4166 | illegal calling convention for constructor/destructor |
| Compiler warning (level 1) C4167 | 'function': only available as an intrinsic function |
| Compiler warning (level 1) C4168 | compiler limit: out of debugger types, delete program database 'database' and rebuild |
| Compiler warning (level 1) C4172 | returning address of local variable or temporary optional_context |
| Compiler warning (level 1) C4174 | 'name': not available as a #pragma component |
| Compiler warning (level 1) C4175 | #pragma component(browser, on): browser info must initially be specified on the command line |
| Compiler warning (level 1) C4176 | 'subcomponent': unknown subcomponent for #pragma component browser |
| Compiler warning (level 1) C4177 | #pragma 'pragma' should only be used at global scope or namespace scope |
| Compiler warning (level 1) C4178 | case constant 'constant' too big for the type of the switch expression |
| Compiler warning (level 4, no longer emitted) C4179 | '//*': parsed as '/' and '/\*': confusion with standard '//' comments |
| Compiler warning (level 1) C4180 | qualifier applied to function type has no meaning; ignored |
| Compiler warning C4181 | qualifier applied to reference type; ignored |
| Compiler warning (level 1) C4182 | #include nesting level is nest_count deep; possible infinite recursion |
| Compiler warning (level 1) C4183 | 'identifier': missing return type; assumed to be a member function returning 'int' |
| Compiler warning (level 1) C4185 | ignoring unknown #import attribute 'attribute' |
| Compiler warning (level 1) C4186 | #import attribute 'attribute' requires 'argument_count' arguments; ignored |
| Compiler warning (level 1) C4187 | #import attributes 'attribute1' and 'attribute2' are incompatible; both ignored |
| Compiler warning (level 1) C4188 | constant expression is not integral |
| Compiler warning (level 3 and level 4) C4189 | 'identifier': local variable is initialized but not referenced |
| Compiler warning (level 1) C4190 | 'identifier1' has C-linkage specified, but returns UDT 'identifier2' which is incompatible with C |
| Compiler warning (level 3, off) C4191 | 'operation': unsafe conversion from 'type_of_expression' to 'type_required' Making a function call using the resulting pointer may cause your program to fail |
| Compiler warning (level 3) C4192 | automatically excluding 'identifier' while importing type library 'library' |
| Compiler warning (level 3) C4193 | #pragma warning(pop): no matching '#pragma warning(push)' |
| Compiler warning (level 1) C4194 | #pragma start_map_region cannot be nested; ignored |
| Compiler warning (level 1) C4195 | #pragma stop_map_region used without matching #pragma start_map_region; ignored |
| Compiler warning (level 1) C4196 | expected 'token1' or 'token2'; found 'token3' |
| Compiler warning (level 3) C4197 | 'type': top-level volatile in cast is ignored |
| Compiler warning (level 1, level 2, level 3, and level 4) C4199 | message |
See also
C/C++ Compiler and build tools errors and warnings
Compiler warnings C4000 - C5999