Microsoft C/C++ compiler warnings C4600 through C4799
The articles in this section describe Microsoft C/C++ compiler warning messages C4600 through C4799.
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 1) C4600 | #pragma 'macro name': expected a valid non-empty string |
| Compiler warning (level 1) C4602 | #pragma pop_macro: 'macro name' no previous #pragma push_macro for this identifier |
| Compiler warning (level 1) C4603 | 'identifier': macro is not defined or definition is different after precompiled header use |
| Compiler warning (level 1) C4604 | 'type': passing argument by value across native and managed boundary requires valid copy constructor. Otherwise the runtime behavior is undefined |
| Compiler warning (level 1) C4605 | '/Dmacro' specified on current command line, but was not specified when precompiled header was built |
| Compiler warning (level 1) C4606 | #pragma warning: 'warning number' ignored; Code Analysis warnings are not associated with warning levels |
| Compiler warning (level 3) C4608 | 'union_member' has already been initialized by another union member in the initializer list, 'union_member' |
| Compiler warning (level 3, Error) C4609 | 'type1' derives from default interface 'interface' on type 'type2'. Use a different default interface for 'type1', or break the base/derived relationship. |
| Compiler warning (level 4) C4610 | object 'class' can never be instantiated - user defined constructor required |
| Compiler warning (level 4) C4611 | interaction between 'function' and C++ object destruction is non-portable |
| Compiler warning (level 1) C4612 | error in include filename |
| Compiler warning (level 1) C4613 | 'symbol': class of segment cannot be changed |
| Compiler warning (level 1) C4615 | #pragma warning: unknown user warning type |
| Compiler warning (level 1) C4616 | #pragma warning: warning number 'number' not a valid compiler warning |
| Compiler warning (level 1) C4618 | pragma parameters included an empty string; pragma ignored |
| Compiler warning (level 3) C4619 | #pragma warning: there is no warning number 'number' |
| Compiler warning (level 1) C4620 | no postfix form of 'operator ++' found for type 'type', using prefix form |
| Compiler warning (level 1) C4621 | no postfix form of 'operator --' found for type 'type', using prefix form |
| Compiler warning (level 3) C4622 | overwriting debug information formed during creation of the precompiled header in object file: 'file' |
| Compiler warning (level 4) C4623 | 'derived class': default constructor was implicitly defined as deleted because a base class default constructor is inaccessible or deleted |
| Compiler warning (level 1) C4624 | 'derived class': destructor was implicitly defined as deleted because a base class destructor is inaccessible or deleted |
| Compiler warning (level 4) C4625 | 'derived class': copy constructor was implicitly defined as deleted because a base class copy constructor is inaccessible or deleted |
| Compiler warning (level 4) C4626 | 'derived class': assignment operator was implicitly defined as deleted because a base class assignment operator is inaccessible or deleted |
| Compiler warning (level 1) C4627 | '<identifier>': skipped when looking for precompiled header use |
| Compiler warning (level 1) C4628 | digraphs not supported with -Ze. Character sequence 'digraph' not interpreted as alternate token for '%s' |
| Compiler warning (level 4) C4629 | digraph used, character sequence 'digraph' interpreted as token 'char' (insert a space between the two characters if this is not what you intended) |
| Compiler warning (level 1) C4630 | 'symbol': 'extern' storage-class specifier illegal on member definition |
| Compiler warning (level 2) C4631 | MSXML or XPath unavailable, XML document comments will not be processed. reason |
| Compiler warning (level 1) C4632 | XML document comment: file - access denied: reason |
| Compiler warning (level 3) C4633 | XML document comment target: error: reason |
| Compiler warning (level 4) C4634 | XML document comment target: cannot be applied: reason |
| Compiler warning (level 3) C4635 | XML document comment target: badly-formed XML: reason |
| Compiler warning (level 3) C4636 | XML document comment applied to construct: tag requires non-empty 'attribute' attribute. |
| Compiler warning (level 3 and level 4) C4637 | XML document comment target: <include> tag discarded. Reason |
| Compiler warning (level 3) C4638 | XML document comment target: reference to unknown symbol 'symbol'. |
| Compiler warning (level 4) C4639 | MSXML error, XML document comments will not be processed. Reason |
| Compiler warning (level 3) C4640 | 'instance': construction of local static object is not thread-safe |
| Compiler warning (level 3) C4641 | XML document comment has an ambiguous cross reference: |
| Compiler warning (level 1) C4642 | 'class': could not import the constraints for generic parameter 'name' |
| Compiler warning (level 4, off) C4643 | Forward declaring 'identifier' in namespace std is not permitted by the C++ Standard. |
| Compiler warning (level 1) C4644 | usage of the macro-based offsetof pattern in constant expressions is non-standard; use offsetof defined in the C++ standard library instead |
| Compiler warning (level 3) C4645 | function declared with __declspec(noreturn) has a return statement |
| Compiler warning (level 3) C4646 | function declared with __declspec(noreturn) has non-void return type |
| Compiler warning (level 3) C4647 | behavior change: __is_pod(type) has different value in previous versions |
| Compiler warning (level 3) C4648 | standard attribute 'carries_dependency' is ignored |
| Compiler warning (level 3) C4649 | attributes are ignored in this context |
| Compiler warning (level 1) C4650 | debugging information not in precompiled header; only global symbols from the header will be available |
| Compiler warning (level 1) C4651 | 'definition' specified for precompiled header but not for current compile |
| Compiler warning (level 1) C4652 | compiler option 'option' inconsistent with precompiled header; current command-line option will override that defined in the precompiled header |
| Compiler warning (level 2) C4653 | compiler option 'option' inconsistent with precompiled header; current command-line option ignored |
| Compiler warning (level 4) C4654 | Code placed before include of precompiled header line will be ignored. Add code to precompiled header. |
| Compiler warning (level 1) C4655 | 'symbol': variable type is new since the latest build, or is defined differently elsewhere |
| Compiler warning (level 1) C4656 | 'symbol': data type is new or has changed since the latest build, or is defined differently elsewhere |
| Compiler warning (level 1) C4657 | expression involves a data type that is new since the latest build |
| Compiler warning (level 1) C4658 | 'function': function prototype is new since the latest build, or is declared differently elsewhere |
| Compiler warning (level 1) C4659 | #pragma 'pragma': use of reserved segment 'segment' has undefined behavior, use #pragma comment(linker, ...) |
| Compiler warning (level 1) C4661 | 'identifier': no suitable definition provided for explicit template instantiation request |
| Compiler warning (level 1) C4662 | explicit instantiation; template-class 'identifier1' has no definition from which to specialize 'identifier2' |
| Compiler warning (level 1) C4667 | 'function': no function template defined that matches forced instantiation |
| Compiler warning (level 4) C4668 | 'symbol' is not defined as a preprocessor macro, replacing with '0' for 'directive' |
| Compiler warning (level 1) C4669 | 'cast': unsafe conversion: 'class' is a managed type object |
| Compiler warning (level 4) C4670 | 'identifier': this base class is inaccessible |
| Compiler warning (level 4) C4671 | 'identifier': the copy constructor is inaccessible |
| Compiler warning (level 4) C4672 | 'identifier1': ambiguous. First seen as 'identifier2' |
| Compiler warning (level 4) C4673 | throwing 'identifier' the following types will not be considered at the catch site |
| Compiler warning (level 1) C4674 | 'method' should be declared 'static' and have exactly one parameter |
| Compiler warning (level 4) C4676 | '%s': the destructor is inaccessible |
| Compiler warning (level 1) C4677 | 'function': signature of non-private member contains assembly private type 'private_type' |
| Compiler warning (level 1) C4678 | base class 'base_type' is less accessible than 'derived_type' |
| Compiler warning (level 1) C4679 | 'member': could not import member |
| Compiler warning (level 4) C4680 | 'class': coclass does not specify a default interface |
| Compiler warning (level 4) C4681 | 'class': coclass does not specify a default interface that is an event source |
| Compiler warning (level 4) C4682 | 'parameter': no directional parameter attribute specified, defaulting to [in] |
| Compiler warning (level 1) C4683 | 'function': event source has an 'out'-parameter; exercise caution when hooking multiple event handlers |
| Compiler warning (level 1) C4684 | 'attribute': WARNING!! attribute may cause invalid code generation: use with caution |
| Compiler warning (level 1) C4685 | expecting '> >' found '>>' when parsing template parameters |
| Compiler warning (level 3) C4686 | 'user-defined type': possible change in behavior, change in UDT return calling convention |
| Compiler warning (Error) C4687 | 'class': a sealed abstract class cannot implement an interface 'interface' |
| Compiler warning (level 1) C4688 | 'constraint': constraint list contains assembly private type 'type' |
| Compiler warning (level 1) C4689 | '%c': unsupported character in #pragma detect_mismatch; #pragma ignored |
| Compiler warning (level 4) C4690 | [ emitidl( pop ) ]: more pops than pushes |
| Compiler warning (level 1) C4691 | 'type': type referenced was expected in unreferenced assembly 'file', type defined in current translation unit used instead |
| Compiler warning (level 1) C4692 | 'function': signature of non-private member contains assembly private native type 'native_type' |
| Compiler warning (level 1, Error) C4693 | 'class': a sealed abstract class cannot have any instance members 'instance member' |
| Compiler warning (level 1, Error) C4694 | 'class': a sealed abstract class cannot have a base-class 'base_class' |
| Compiler warning (level 1) C4695 | #pragma execution_character_set: 'character set' is not a supported argument: currently only 'UTF-8' is supported |
| Compiler warning (level 1) C4696 | /ZBvalue1 option out of range; assuming 'value2' |
| Compiler warning (level 3) C4698 | 'feature' is for evaluation purposes only and is subject to change or removal in future updates. |
| Compiler warning (level 1 and level 4) C4700 | uninitialized local variable 'name' used |
| Compiler warning (level 4) C4701 | potentially uninitialized local variable 'name' used |
| Compiler warning (level 4) C4702 | unreachable code |
| Compiler warning (level 4) C4703 | potentially uninitialized local pointer variable '%s' used |
| Compiler warning (level 4) C4706 | assignment within conditional expression |
| Compiler warning (level 4) C4709 | comma operator within array index expression |
| Compiler warning (level 4) C4710 | 'function': function not inlined |
| Compiler warning (level 1) C4711 | function 'function' selected for automatic inline expansion |
| Compiler warning (level 4) C4714 | function 'function' marked as __forceinline not inlined |
| Compiler warning (level 1) C4715 | 'function': not all control paths return a value |
| Compiler warning (level 1, Error) C4716 | 'function': must return a value |
| Compiler warning (level 1) C4717 | 'function': recursive on all control paths, function will cause runtime stack overflow |
| Compiler warning (level 4) C4718 | 'function call': recursive call has no side effects, deleting |
| Compiler warning (level 1) C4719 | Double constant found when Qfast specified - use 'f' as a suffix to indicate single precision |
| Compiler warning (level 2) C4720 | in-line assembler reports: 'message' |
| Compiler warning (level 1) C4721 | 'function': not available as an intrinsic |
| Compiler warning (level 1) C4722 | 'function': destructor never returns, potential memory leak |
| Compiler warning (level 3) C4723 | potential divide by 0 |
| Compiler warning (level 3) C4724 | potential mod by 0 |
| Compiler warning (level 3) C4725 | instruction may be inaccurate on some Pentiums |
| Compiler warning C4726 | ARM arch4/4T supports only '<cpsr_f> or <spsr_f>' with immediate value |
| Compiler warning (level 1) C4727 | PCH named pch_file with same timestamp found in obj_file_1 and obj_file_2. Using first PCH. |
| Compiler warning (level 1) C4728 | /Yl- option ignored because PCH reference is required |
| Compiler warning (level 4) C4729 | function too big for flow graph based warnings |
| Compiler warning (Level 1) C4730 | 'main': mixing _m64 and floating point expressions may result in incorrect code |
| Compiler warning (Level 1) C4731 | 'pointer': frame pointer register 'register' modified by inline assembly code |
| Compiler warning (level 1) C4732 | intrinsic '%s' is not supported in this architecture |
| Compiler warning (Level 1) C4733 | Inline asm assigning to 'FS:0': handler not registered as safe handler |
| Compiler warning C4734 | More than 64k line numbers in a COFF debug info section; stop emitting COFF debug line numbers for module 'module' |
| Compiler warning C4735 | align_function attribute argument 'argument' is not a power of two and is not positive. Ignoring attribute |
| Compiler warning C4736 | align_function attribute ignored because /Gy was not specified |
| Compiler warning (Level 3) C4738 | storing 32-bit float result in memory, possible loss of performance |
| Compiler warning (level 1) C4739 | reference to variable 'var' exceeds its storage space |
| Compiler warning (Level 4) C4740 | flow in or out of inline asm code suppresses global optimization |
| Compiler warning (Level 1) C4742 | 'var' has different alignment in 'file1' and 'file2': number and number |
| Compiler warning (Level 1) C4743 | 'type' has different size in 'file1' and 'file2': number and number bytes |
| Compiler warning (Level 1) C4744 | 'var' has different type in 'file1' and 'file2': 'type1' and 'type2' |
| Compiler warning C4745 | volatile access of 'name' cannot be honored due to its size |
| Compiler warning C4746 | volatile access of 'expression' is subject to /volatile:<iso|ms> setting; consider using __iso_volatile_load/store intrinsic functions |
| Compiler warning (level 1) C4747 | Calling managed 'entrypoint': Managed code may not be run under loader lock, including the DLL entrypoint and calls reached from the DLL entrypoint |
| Compiler warning (level 4) C4749 | conditionally supported: offsetof applied to non-standard-layout type 'type' |
| Compiler warning (level 1) C4750 | 'identifier': function with _alloca() inlined into a loop |
| Compiler warning (level 4) C4751 | /arch:AVX does not apply to Intel(R) Streaming SIMD Extensions that are within inline ASM |
| Compiler warning (level 4) C4752 | found Intel(R) Advanced Vector Extensions; consider using /arch:AVX |
| Compiler warning C4753 | Cannot find bounds for pointer; MPX intrinsic function ignored |
| Compiler warning (level 4) C4754 | Conversion rules for arithmetic operations in the comparison at %s(%d) mean that one branch cannot be executed. Cast '%s' to '%s' (or similar type of %d bytes). |
| Compiler warning C4755 | Conversion rules for arithmetic operations in the comparison at %s(%d) mean that one branch cannot be executed in an inlined function. Cast '%s' to '%s' (or similar type of %d bytes). |
| Compiler warning (level 2) C4756 | overflow in constant arithmetic |
| Compiler warning (level 4) C4757 | subscript is a large unsigned value, did you intend a negative constant? |
| Compiler warning C4761 | integral size mismatch in argument; conversion supplied |
| Compiler warning (level 4) C4764 | Can not align catch objects to greater than 16 bytes |
| Compiler warning (level 4) C4767 | section name '%s' is longer than 8 characters and will be truncated by the linker |
| Compiler warning (level 3) C4768 | __declspec attributes before linkage specification are ignored |
| Compiler warning (level 4) C4770 | partially validated enum 'name' used as index |
| Compiler warning C4771 | Bounds must be created using a simple pointer; MPX intrinsic function ignored |
| Compiler warning (level 1, Error) C4772 | #import referenced a type from a missing type library; 'missing_type' used as a placeholder |
| Compiler warning (level 4) C4774 | 'string' : format string expected in argument number is not a string literal |
| Compiler warning (level 3) C4775 | nonstandard extension used in format string 'string' of function 'function' |
| Compiler warning (level 1) C4776 | '%character' is not allowed in the format string of function 'function' |
| Compiler warning (level 4) C4777 | 'function' : format string 'string' requires an argument of type 'type1', but variadic argument number has type 'type2' |
| Compiler warning (level 3) C4778 | 'function' : unterminated format string 'string' |
| Compiler warning (Level 1) C4788 | 'identifier': identifier was truncated to 'number' characters |
| Compiler warning (Level 1) C4789 | buffer 'identifier' of size N bytes will be overrun; M bytes will be written starting at offset L |
| Compiler warning (level 2) C4792 | function '%s' declared using sysimport and referenced from native code; import library required to link |
| Compiler warning (level 1 and 3) C4793 | 'function': function compiled as native: 'reason' |
| Compiler warning (level 1) C4794 | segment of thread local storage variable '%s' changed from '%s' to '%s' |
| Compiler warning C4798 | native code generated for p-code function 'name' with exception handler or unwind semantics |
| Compiler warning (level 1) C4799 | function 'function' has no EMMS instruction |
See also
C/C++ Compiler and build tools errors and warnings
Compiler warnings C4000 - C5999