Microsoft C/C++ compiler warnings C4800 through C4999
The articles in this section describe Microsoft C/C++ compiler warning messages C4800-C4999.
Important
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Note
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Warning messages
| Warning | Message |
|---|---|
| Compiler warning (level 4, off) C4800 | Implicit conversion from 'type' to bool. Possible information loss |
| Compiler warning C4801 | Return by reference is not verifiable: message |
| Compiler warning (level 1) C4803 | 'method': the raise method has a different storage class from that of the event, 'event' |
| Compiler warning (level 1) C4804 | 'operation': unsafe use of type 'bool' in operation |
| Compiler warning (level 1) C4805 | 'operation': unsafe mix of type 'type1' and type 'type2' in operation |
| Compiler warning (level 1) C4806 | 'operation': unsafe operation: no value of type 'type1' promoted to type 'type2' can equal the given constant |
| Compiler warning (level 1) C4807 | 'operation': unsafe mix of type 'type1' and signed bit field of type 'type2' |
| Compiler warning (level 1) C4808 | case 'value' is not a valid value for switch condition of type 'bool' |
| Compiler warning (level 1) C4809 | switch statement has redundant 'default' label; all possible 'case' labels are given |
| Compiler warning (level 1) C4810 | value of pragma pack(show) == n |
| Compiler warning (level 1) C4811 | value of pragma conform(forScope, show) == value |
| Compiler warning (level 1) C4812 | obsolete declaration style: please use 'new_syntax' instead |
| Compiler warning (level 1) C4813 | 'function': a friend function of a local class must have been previously declared |
| Compiler warning (level 4) C4815 | 'object name': zero-sized array in stack object will have no elements (unless the object is an aggregate that has been aggregate initialized) |
| Compiler warning (level 4) C4816 | 'param': parameter has a zero-sized array which will be truncated (unless the object is passed by reference) |
| Compiler warning (level 1) C4817 | 'member': illegal use of '.' to access this member; compiler replaced with '->' |
| Compiler warning (level 1) C4819 | The file contains a character that cannot be represented in the current code page (number). Save the file in Unicode format to prevent data loss |
| Compiler warning (level 4, off) C4820 | 'bytes' bytes padding added after construct 'member_name' |
| Compiler warning (level 1) C4821 | Unable to determine Unicode encoding type, please save the file with signature (BOM) |
| Compiler warning (level 1, off) C4822 | 'member function': local class member function does not have a body |
| Compiler warning (level 3) C4823 | 'function': uses pinning pointers but unwind semantics are not enabled. Consider using /EHa |
| Compiler warning (level 2, off) C4826 | Conversion from 'type1' to 'type2' is sign-extended. This may cause unexpected runtime behavior. |
| Compiler warning (level 3) C4827 | A public 'ToString' method with 0 parameters should be marked as virtual and override |
| Compiler warning (level 1) C4828 | The file contains a character starting at offset 0xHexOffset that is illegal in the current source character set (codepage codepage). |
| Compiler warning (level 1) C4829 | Possibly incorrect parameters to function main. Consider 'int main(Platform::Array<Platform::String^>^ argv)' |
| Compiler warning (level 1) C4834 | discarding return value of function with 'nodiscard' attribute |
| Compiler warning (level 1) C4835 | 'variable': the initializer for exported data will not be run until managed code is first executed in the host assembly |
| Compiler warning (level 4, off) C4837 | trigraph detected: '??character' replaced by 'character' |
| Compiler warning (level 1) C4838 | conversion from 'type_1' to 'type_2' requires a narrowing conversion |
| Compiler warning (level 3) C4839 | non-standard use of class 'type' as an argument to a variadic function |
| Compiler warning (level 4) C4840 | non-portable use of class 'type' as an argument to a variadic function |
| Compiler warning (level 4, off) C4841 | non-standard extension used: compound member designator used in offsetof |
| Compiler warning (level 4, off) C4842 | the result of 'offsetof' applied to a type using multiple inheritance is not guaranteed to be consistent between compiler releases |
| Compiler warning (level 4) C4843 | 'type1': An exception handler of reference to array or function type is unreachable, use 'type2' instead |
| Compiler warning (level 1) C4844 | 'export module module_name;' is now the preferred syntax for declaring a module interface |
| Compiler warning (level 4) C4845 | '__declspec(no_init_all)' is ignored if '/d1initall[0|1|2|3]' was not specified on the command line |
| Compiler warning (level 4) C4846 | 'value' is not a valid argument for '/d1initall': command-line flag ignored |
| Compiler warning (level 4) C4847 | '__declspec(no_init_all)' can only be applied to a function, a class type, or a local variable: ignored |
| Compiler warning (level 1) C4848 | support for standard attribute 'no_unique_address' in C++17 and earlier is a vendor extension |
| Compiler warning (level 1) C4849 | OpenMP 'clause' clause ignored in 'directive' directive |
| Compiler warning (Level 1, error) C4854 | binding dereferenced null pointer to reference has undefined behavior |
| Compiler warning (level 1, off) C4855 | implicit capture of 'this' via '[=]' is deprecated in 'version' |
| Compiler warning (level 4) C4856 | 'value' is not a valid argument for '/d1initAll:FillPattern' (value must be between 0 and 255). Command-line flag ignored |
| Compiler warning (level 1) C4857 | C++/CLI mode does not support C++ versions newer than C++17; setting language to /std:c++17 |
| Compiler warning (level 1) C4858 | discarding return value: function name |
| Compiler warning (level 4) C4859 | 'value' is not a valid argument for '/presetWarn': it must be a decimal value > 0. Command-line flag ignored |
| Compiler warning (level 4) C4860 | 'object name': compiler zero initialized 'number' bytes of storage |
| Compiler warning (level 4) C4861 | compiler zero initialized 'number' bytes of storage |
| Compiler warning (level 4) C4866 | compiler may not enforce left-to-right evaluation order for call to operator_name |
| Compiler warning (level 1, error) C4867 | 'function': function call missing argument list; use 'call' to create a pointer to member |
| Compiler warning (level 4) C4868 | 'file(line_number)' compiler may not enforce left-to-right evaluation order in braced initialization list |
| Compiler warning (level 3) C4869 | 'nodiscard' may only be applied to classes, enumerations, and functions |
| Compiler warning (level 2) C4872 | floating point division by zero detected when compiling the call graph for the concurrency::parallel_for_each at: 'location' |
| Compiler warning (level 1) C4880 | casting from 'const type_1' to 'type_2': casting away constness from a pointer or reference may result in undefined behavior in an amp restricted function |
| Compiler warning (level 4) C4881 | the constructor and/or the destructor will not be invoked for tile_static variable 'variable-name' |
| Compiler warning (level 1) C4882 | passing functors with non-const call operators to concurrency::parallel_for_each is deprecated |
| Compiler warning C4883 | 'function name': function size suppresses optimizations |
| Compiler warning C4900 | Il mismatch between 'tool1' version 'version1' and 'tool2' version 'version2' |
| Compiler warning (level 1, off) C4905 | wide string literal cast to 'LPSTR' |
| Compiler warning (level 1, off) C4906 | string literal cast to 'LPWSTR' |
| Compiler warning (Error) C4907 | multiple calling conventions cannot be specified; last given will be used |
| Compiler warning (level 1) C4910 | '<identifier>: '__declspec(dllexport)' and 'extern' are incompatible on an explicit instantiation |
| Compiler warning (level 1) C4912 | 'attribute': attribute has undefined behavior on a nested UDT |
| Compiler warning (level 4) C4913 | user defined binary operator ',' exists but no overload could convert all operands, default built-in binary operator ',' used |
| Compiler warning (level 1) C4916 | in order to have a dispid, 'description': must be introduced by an interface |
| Compiler warning (level 1, off) C4917 | 'declarator': a GUID can only be associated with a class, interface or namespace |
| Compiler warning (level 4) C4918 | 'character': invalid character in pragma optimization list |
| Compiler warning (level 1) C4920 | enum enum-name member member_1=value_1 already seen in enum enum-name as member_2=value_2 |
| Compiler warning (level 3) C4921 | 'description': attribute value 'attribute' should not be multiply specified |
| Compiler warning (level 1) C4925 | 'method': dispinterface method cannot be called from script |
| Compiler warning (level 1) C4926 | 'identifier': symbol is already defined: attributes ignored |
| Compiler warning (level 1) C4927 | illegal conversion; more than one user-defined conversion has been implicitly applied |
| Compiler warning (level 1, off) C4928 | illegal copy-initialization; more than one user-defined conversion has been implicitly applied |
| Compiler warning (level 1) C4929 | 'file': typelibrary contains a union; ignoring the 'embedded_idl' qualifier |
| Compiler warning (level 1) C4930 | 'prototype': prototyped function not called (was a variable definition intended?) |
| Compiler warning (level 4, off) C4931 | we are assuming the type library was built for number-bit pointers |
| Compiler warning (level 4) C4932 | __identifier(identifier) and __identifier(identifier) are indistinguishable |
| Compiler warning (level 1) C4934 | '__delegate(multicast)' is deprecated, use '__delegate' instead |
| Compiler warning (level 1) C4935 | assembly access specifier modified from 'access' |
| Compiler warning (level 1, Error) C4936 | this __declspec is supported only when compiled with /clr or /clr:pure |
| Compiler warning (level 4) C4937 | 'text1' and 'text2' are indistinguishable as arguments to 'directive' |
| Compiler warning (level 4) C4938 | 'var': Floating point reduction variable may cause inconsistent results under /fp:strict or #pragma fenv_access |
| Compiler warning C4939 | #pragma vtordisp is deprecated and will be removed in a future release of Visual C++ |
| Compiler warning (level 1) C4944 | 'symbol': cannot import symbol from 'assembly1': as 'symbol' already exists in the current scope |
| Compiler warning (level 1) C4945 | 'symbol': cannot import symbol from 'assembly1': as 'symbol' has already been imported from another assembly 'assembly2' |
| Compiler warning (level 1, off) C4946 | reinterpret_cast used between related classes: 'class1' and 'class2' |
| Compiler warning (level 1) C4947 | 'type_or_member': marked as obsolete |
| Compiler warning (level 2) C4948 | return type of 'accessor' does not match the last parameter type of the corresponding setter |
| Compiler warning (level 1 and level 4) C4949 | pragmas 'managed' and 'unmanaged' are meaningful only when compiled with '/clr[:option]' |
| Compiler warning (level 1, Error) C4950 | 'type_or_member': marked as obsolete |
| Compiler warning (level 1) C4951 | 'function' has been edited since profile data was collected, function profile data not used |
| Compiler warning (level 1) C4952 | 'function': no profile data found in program database 'pgd-file' |
| Compiler warning (level 1) C4953 | Inlinee 'function' has been edited since profile data was collected, profile data not used |
| Compiler warning C4954 | 'function': not profiled (contains __int64 switch expression) |
| Compiler warning C4955 | 'import2': import ignored; already imported from 'import1' |
| Compiler warning (level 1, Error) C4956 | 'type': this type is not verifiable |
| Compiler warning (level 1, Error) C4957 | 'cast': explicit cast from 'cast_from' to 'cast_to' is not verifiable |
| Compiler warning (level 1, Error) C4958 | 'operation': pointer arithmetic is not verifiable |
| Compiler warning (level 1, Error) C4959 | cannot define unmanaged type 'type' in /clr:safe because accessing its members yields unverifiable code |
| Compiler warning (level 4) C4960 | 'function' is too big to be profiled |
| Compiler warning (level 1) C4961 | No profile data was merged into 'pgd-file', profile-guided optimizations disabled |
| Compiler warning (level 4, off) C4962 | 'function': Profile-guided optimizations disabled because optimizations caused profile data to become inconsistent |
| Compiler warning (level 1) C4963 | 'description': no profile data found; different compiler options were used in instrumented build |
| Compiler warning (level 1) C4964 | No optimization options were specified; profile info will not be collected |
| Compiler warning (level 1) C4965 | implicit box of integer 0; use nullptr or explicit cast |
| Compiler warning (level 1) C4966 | 'function' has __code_seg annotation with unsupported segment name, annotation ignored |
| Compiler warning C4970 | delegate constructor: target object ignored since 'type' is static |
| Compiler warning (level 1) C4971 | Argument order: <target object>, <target function> for delegate constructor is deprecated, use <target function>, <target object=""> |
| Compiler warning (level 1, Error) C4972 | Directly modifying or treating the result of an unbox operation as an lvalue is unverifiable |
| Compiler warning (level 1) C4973 | 'symbol': marked as deprecated |
| Compiler warning (level 1) C4974 | 'symbol': marked as deprecated |
| Compiler warning (level 1) C4975 | modopt '[modifier]' was ignored for formal parameter 'parameter' |
| Compiler warning (level 1) C4976 | invalid value 'value' for '/W'; assuming '1' |
| Compiler warning (level 3) C4981 | Warbird: function 'function' marked as __forceinline not inlined because it contains exception semantics |
| Compiler warning (level 3) C4983 | '/analyze:sarif:hashname' ignored because the argument to '/analyze:log' is a single file rather than a directory |
| Compiler warning C4984 | 'if constexpr' is a C++17 language extension |
| Compiler warning (level 4) C4985 | 'symbol_name': attributes not present on previous declaration. |
| Compiler warning (level 4, off) C4986 | 'declaration': exception specification does not match previous declaration |
| Compiler warning (level 4, off) C4987 | nonstandard extension used: 'throw (...)' |
| Compiler warning (level 4, off) C4988 | 'variable': variable declared outside class/function scope |
| Compiler warning (level 4) C4989 | 'type': type has conflicting definitions. |
| Compiler warning (level 3) C4990 | Warbird: message |
| Compiler warning (level 3) C4991 | Warbird: function 'function' marked as __forceinline not inlined because protection level of inlinee is greater than the parent |
| Compiler warning (level 3) C4992 | Warbird: function 'function-name' marked as __forceinline not inlined because it contains inline assembly which cannot be protected |
| Compiler warning (level 3) C4995 | 'function': name was marked as #pragma deprecated |
| Compiler warning (level 3) C4996 | 'deprecated-declaration': deprecation-message (or "was declared deprecated") |
| Compiler warning (level 1) C4997 | 'class': coclass does not implement a COM interface or pseudo-interface |
| Compiler warning (level 1) C4998 | EXPECTATION FAILED: expectation(value) |
See also
C/C++ Compiler and build tools errors and warnings
Compiler warnings C4000 - C5999