Missing ‘#include ‘; ‘ucontext64_t’ must be declared before it is used

Hello Guys,
In this article, we are going to see the solution for the iOS error:
Missing '#include <sys/_types/_ucontext64.h>'; 'ucontext64_t' must be declared before it is used

This error commonly occurs when working with lower-level C/C++ or Objective-C(++) files on Apple platforms, especially in contexts involving crash handling, signal contexts, or working directly with the ucontext64_t structure on Apple Silicon (arm64).

1. Error Description

When building your iOS/macOS project, you might see a compilation error like:

Missing '#include <sys/_types/_ucontext64.h>'; 'ucontext64_t' must be declared before it is used

This means the compiler doesn’t recognize the type ucontext64_t because its definition has not been included in your file.

2. Why it happens?

• ucontext64_t is an internal type used in Apple’s Darwin system, often only exposed in certain contexts, or private headers.

• If you’re working on crash reporting, signal handling, or thread context manipulation (like using Sentry, KSCrash, etc.), and targeting Apple Silicon, this type is needed.

3. Error Solution:

Here are some ways to resolve it:

1. Use the correct import manually

If your code runs only on Apple platforms, you can include the internal header:

#include <sys/_types/_ucontext64.h>

Note: This is considered a private header, so use it carefully and test across all target iOS/macOS versions.

2. Use conditional imports

Wrap the import in a platform check to ensure it only compiles on supported platforms:

#ifdef __APPLE__
  #include <sys/_types/_ucontext64.h>
#endif

3. Check architecture

Make sure this is only used for arm64 architecture:

#ifdef __arm64__
  typedef ucontext64_t SignalUserContext;
#else
  typedef ucontext_t SignalUserContext;
#endif

#ifdef __arm64__
#    define UC_MCONTEXT uc_mcontext64
typedef ucontext64_t SignalUserContext;
#else
#    define UC_MCONTEXT uc_mcontext
typedef ucontext_t SignalUserContext;
#endif

#include <sys/ucontext.h> // For ucontext_t and related types

#ifdef __arm64__
#    define UC_MCONTEXT uc_mcontext
typedef ucontext_t SignalUserContext;
#else
#    define UC_MCONTEXT uc_mcontext
typedef ucontext_t SignalUserContext;
#endif