Microsoft C/C++ compiler warnings C5200 through C5399
The articles in this section describe Microsoft C/C++ compiler warning messages C5200 through C5399.
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.
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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 1) C5200 | feature 'feature-name' requires compiler flag 'option-name' |
| Compiler warning (level 1) C5201 | a module declaration can appear only at the start of a translation unit unless a global module fragment is used |
| Compiler warning (level 1) C5202 | a global module fragment can only contain preprocessor directives |
| Compiler warning (level 1) C5203 | a parenthesized declarator name after 'explicit' will be considered an explicit-specifier in C++20 |
| Compiler warning (level 3, off) C5204 | 'type-name': class has virtual functions, but its trivial destructor is not virtual; instances of objects derived from this class may not be destructed correctly |
| Compiler warning (level 4) C5205 | delete of an abstract class 'type-name' that has a non-virtual destructor results in undefined behavior |
| Compiler warning (level 3) C5206 | deduced return types for coroutines is a non-standard extension |
| Compiler warning (level 1) C5207 | the simple requirement asserts the validity of expression 'e->id'. Did you mean '{ e } -> id'? You can suppress the warning using '{ e->id }' |
| Compiler warning (level 1) C5208 | unnamed class used in typedef name cannot declare members other than non-static data members, member enumerations, or member classes |
| Compiler warning (level 1) C5209 | the C++20 syntax for an init-capture has changed to '& ...opt identifier initializer' |
| Compiler warning (level 1) C5210 | 'name' is not a valid header unit reference; ignoring |
| Compiler warning (level 1) C5212 | 'name' is not a valid named reference; treating as reference to file |
| Compiler warning (level 1) C5213 | 'name' named reference is treated as a named partition but the name is not specified; treating as reference to file |
| Compiler warning (level 4, off) C5214 | applying 'modifier' to an operand with a volatile qualified type is deprecated in C++20 |
| Compiler warning (level 4, off) C5215 | 'name' a function parameter with a volatile qualified type is deprecated in C++20 |
| Compiler warning (level 4, off) C5216 | 'name' a volatile qualified return type is deprecated in C++20 |
| Compiler warning (level 4, off) C5217 | a structured binding declaration that includes volatile is deprecated in C++20 |
| Compiler warning (level 1) C5218 | destroying delete may not behave as intended when non-conforming switches '/Zc:sizedDealloc-' or '/Zc:alignedNew-' are used |
| Compiler warning (level 2, off) C5219 | implicit conversion from 'type-1' to 'type-2', possible loss of data |
| Compiler warning (level 4, off) C5220 | 'name': a non-static data member with a volatile qualified type no longer implies that compiler generated copy/move constructors and copy/move assignment operators are not trivial |
| Compiler warning (level 1) C5221 | xfg::rename is deprecated. |
| Compiler warning (level 3) C5222 | 'attribute-name': all unscoped attribute names are reserved for future standardization |
| Compiler warning (level 3) C5223 | all attribute names in the attribute namespace 'msvc' are reserved for the implementation |
| Compiler warning (level 3) C5224 | all attribute names in the attribute namespace 'namespace-name' are reserved for future standardization |
| Compiler warning (level 1) C5225 | 'symbol': exported inline function defined in a private module fragment is a non-standard extension |
| Compiler warning (level 1) C5226 | 'symbol': exported template defined in private module fragment has no reachable instantiation |
| Compiler warning (level 4) C5227 | nonstandard extension, resolved 'symbol' to 'value' which is not visible with /permissive- on. |
| Compiler warning (level 4) C5228 | nonstandard extension, 'identifier' resolved to a member of a dependent base. This lookup is not allowed under /permissive-. |
| Compiler warning (level 4) C5229 | nonstandard extension, the hidden friend function 'function-name' was found by name lookup which isn't allowed under /permissive-. |
| Compiler warning C5230 | nonstandard extension, 'identifier' was resolved to 'symbol-1' under /permissive. Under /permissive- it would resolve to 'symbol-2'. |
| Compiler warning (level 3) C5231 | the expression 'co_await promise.final_suspend()' must be non-throwing |
| Compiler warning (level 1) C5232 | in C++20 this comparison calls 'name' recursively |
| Compiler warning (level 4, off) C5233 | explicit lambda capture 'identifier' is not used |
| Compiler warning (level 1) C5234 | file system error: 'filename' is not a valid header-name; ignoring |
| Compiler warning (level 1) C5235 | JSON parse error: message; ignoring 'filename' |
| Compiler warning (level 1) C5236 | JSON ill-formed: message; ignoring 'filename' |
| Compiler warning (level 1) C5237 | cannot resolve header unit entry 'name' to a header file in 'filename'; ignoring entry |
| Compiler warning (level 1) C5238 | file system error: cannot open 'filename' for reading; ignoring |
| Compiler warning (level 4) C5239 | 'symbol': potentially throwing function called from a function declared __declspec(nothrow). Undefined behavior may occur if an exception is thrown. |
| Compiler warning (level 4) C5240 | 'attribute-name': attribute is ignored in this syntactic position |
| Compiler warning (level 1) C5241 | '/exportHeader' usage to lookup header-name is deprecated; prefer '/headerName:name value=filename' |
| Compiler warning (level 1) C5242 | syntax error in pragma 'identifier' |
| Compiler warning (level 1, off) C5243 | 'type-name': using incomplete class 'class-name' can cause potential one definition rule violation due to ABI limitation |
| Compiler warning (level 1) C5244 | '#include <filename>' in the purview of module 'module-name-1' appears erroneous. Consider moving that directive before the module declaration, or replace the textual inclusion with 'import <module-name-2>;'. |
| Compiler warning (level 4, off) C5245 | 'function': unreferenced function with internal linkage has been removed |
| Compiler warning (level 1, off) C5246 | 'member': the initialization of a subobject should be wrapped in braces |
| Compiler warning (level 1, off) C5247 | section 'section-name' is reserved for C++ dynamic initialization. Manually creating the section will interfere with C++ dynamic initialization and may lead to undefined behavior |
| Compiler warning (level 1, off) C5248 | section 'section-name' is reserved for C++ dynamic initialization. Variables manually put into the section may be optimized out and their order relative to compiler generated dynamic initializers is unspecified. |
| Compiler warning (level 1, off) C5249 | 'bitfield' of type 'enumeration_name' has named enumerators with values that cannot be represented in the given bit field width of 'bitfield_width'. |
| Compiler warning (level 3, off) C5250 | 'function_name': intrinsic function not declared. |
| Compiler warning (level 4, off) C5251 | segment-name changed after including header |
| Compiler warning (level 4) C5252 | Multiple different types resulted in the same XFG type-hash hash-value; the PDB will only record information for one of them |
| Compiler warning (level 4) C5253 | a non-local lambda cannot have a capture default |
| Compiler warning (level 4, off) C5254 | language feature 'terse static assert' requires compiler flag '/std:c++17' |
| Compiler warning (level 3) C5255 | unterminated bidirectional character encountered: 'U+XXXX' |
| Compiler warning (level 1, off) C5256 | 'enumeration': a non-defining declaration of an enumeration with a fixed underlying type is only permitted as a standalone declaration |
| Compiler warning (level 1 or 4) C5257 | 'enumeration': enumeration was previously declared without a fixed underlying type |
| Compiler warning (level 4, off) C5258 | explicit capture of 'symbol' is not required for this use |
| Compiler warning (level 4, off) C5259 | 'specialized-type': explicit specialization requires 'template <>' |
| Compiler warning (level 1) C5260 | the constant variable 'variable-name' has internal linkage in an included header file context, but external linkage in imported header unit context; consider declaring it 'inline' as well if it will be shared across translation units, or 'static' to express intent to use it local to this translation unit |
| Compiler warning (level 2) C5261 | no integer type can represent all enumerator values in enumeration 'enum-name' |
| Compiler warning (level 1, error, off) C5262 | implicit fall-through occurs here; are you missing a break statement? Use [[fallthrough]] when a break statement is intentionally omitted between cases |
| Compiler warning (level 4, off) C5263 | calling 'std::move' on a temporary object prevents copy elision |
| Compiler warning (level 4, off) C5264 | 'variable-name': 'const' variable is not used |
| Compiler warning (level 1) C5265 | cannot open search path 'path' |
| Compiler warning (level 4, off) C5266 | 'const' qualifier on return type has no effect |
| Compiler warning C5267 | definition of implicit copy constructor/assignment operator for 'type' is deprecated because it has a user-provided assignment operator/copy constructor |
| Compiler warning (level 1) C5268 | Failed to allocate memory at fixed address 0xaddress. Use /Yb to specify a specific address base if bit-identical .pch files are required. |
| Compiler warning (level 1) C5269 | Failed to allocate PCH memory at fixed address 0xaddress. Use /Ym to specify a specific address base if bit-identical .pch files are required. |
| Compiler warning (level 3) C5270 | 'value' is not allowed for option 'switch name'; allowed values are: value list |
| Compiler warning (level 4) C5271 | previously imported assembly 'assembly1' has the same name as assembly 'assembly2' being imported. Is this intentional? |
| Compiler warning (level 1) C5272 | throwing an object of non-copyable type 'type' is non-standard. If a copy is needed at runtime it will be made as if by memcpy. |
| Compiler warning (level 1) C5273 | behavior change: _Alignas on anonymous type no longer ignored (promoted members will align) |
| Compiler warning (level 1) C5274 | behavior change: _Alignas no longer applies to the type 'type' (only applies to declared data objects) |
| Compiler warning (Error) C5275 | facade assembly 'name' being imported under '/clr'; missing option '/clr:netcore'? |
| Compiler warning (level 1, error) C5300 | '#pragma omp atomic': left operand of 'operator' must match left hand side of assignment-expression |
| Compiler warning (level 1) C5301 | '#pragma omp for': 'loop-index' increases while loop condition uses 'comparison'; non-terminating loop? |
| Compiler warning (level 1) C5302 | '#pragma omp for': 'loop-index' decreases while loop condition uses 'comparison'; non-terminating loop? |
| Compiler warning (level 1) C5303 | function marked with [[msvc::intrinsic]] did not result in a no-op cast |
| Compiler warning (level 1) C5304 | a declaration designated by the using-declaration 'name1' exported from this module has internal linkage and using such a name outside the module is ill-formed; consider declaring 'name2' 'inline' to use it outside of this module |
| Compiler warning (level 1) C5305 | 'name': an explicit instantiation declaration that follows an explicit instantiation definition is ignored |
See also
C/C++ Compiler and build tools errors and warnings
Compiler warnings C4000 - C5999