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std::print String Segfault: Is It a Compiler Bug?

Why does std::print segfault on ARM64 with string? Explore possible causes like undefined behavior or GCC trunk issues.

byDev Solutions

January 22, 2026

Thumbnail image showing std::print causing segfault on ARM64 with C++ code and a glowing ARM64 CPU alongside GCC warning signs and crash error text.

⚠️ GCC trunk builds on ARM64 can cause std::print to segfault when handling std::string.
🧠 The issue is not due to undefined behavior in user code but likely stems from incomplete or buggy standard library implementations.
📈 ARM64 platforms now represent over 13% of global laptop shipments, increasing exposure to architecture-specific bugs.
💻 Workarounds like using s.c_str() or falling back to std::format can prevent crashing in unstable builds.
🛠️ Reporting reproducible segfaults to GCC’s Bugzilla helps improve compiler stability across platforms.

A Dangerous Change: When `std::print` Has Issues

C++23 brought in std::print to make output formatting better. It brought together safety during compilation with new ways to write code. It was supposed to make writing strong code easier. But developers quickly found that this new feature could cause a segfault on ARM64 when compiled with a trunk version of GCC. In this article, we'll look closely at where this bug comes from. We will also look at the machine setup and tools involved. And then we will give clear ways to work around or avoid these issues in your C++23 work.

The Power and Pitfalls of `std::print`

C++ developers have for a long time used old ways like printf or long streams (std::cout) to show output. These tools were either likely to have errors or could not be easily put together with other parts. std::format came in C++20. This changed things towards formatting that could be put together and was safe with types. And then with C++23, std::print continues that progress. Now, developers can send formatted output right to the standard output with very little work.

What Makes `std::print` Appealing?

The std::print function has several good points for developers:

Type Safety: Errors with formatting show up when you compile, and this stops dangerous crashes when the program runs.
Cleaner Syntax: This makes code clearer and not too long.
Consistency: It is based on std::format, and it makes sure output works the same way every time and can be used again.
Performance: It lets you format things that are known at compile time when used with exact formats.

A Side-by-Side Comparison

To see how things got better, let’s look at how different ways to show output work in real use:

#include <cstdio>     // C-style
#include <format>     // C++20 format
#include <print>      // C++23 print
#include <iostream>
#include <string>

std::string hello = "world";

// C-style
printf("%s\n", hello.c_str());

// C++20
std::cout << std::format("{}\n", hello);

// C++23
std::print("{}\n", hello);

The last line shows what std::print truly offers for getting things done: short code, built-in safety, and how it fits with new C++ ideas.

But under its clean look, problems can start. This is especially true when compilers and platforms are not current.

How a Segfault Happens: The ARM64 Crash

Imagine this fuller example:

#include <print>
#include <string>

int main() {
    std::string s = "hello";
    std::print("{}\n", s);  // Causes a segfault on some systems
}

When compiled on an ARM64 machine using a GCC trunk build (this is a pre-release version of the GNU compiler for testing), this code can cause a segmentation fault when it runs. The crash usually happens deep in the formatting part, not inside any code you wrote.

Understanding `Segfault`

A segmentation fault generally means the program attempted to read or write to a memory location it's not allowed to access. If it crashes inside a standard library call while formatting a properly set up std::string, this shows that the compiler and library do not match up right for your system.

Root Causes: Undefined Behavior or Compiler Mistakes

The first step in fixing a std::print segfault issue is to find out if it's your fault, or the compiler's.

✅ Why the Code Is Sound

You're using a valid std::string
The format string {} is syntactically correct
You're not formatting pointers or structs that lack formatter overloads
There's no multithreading or race conditions happening.

All of these things suggest you are not causing undefined behavior. So, the most likely explanations are these:

Compiler Bug: A trunk (very new) compiler compiled your program wrong.
Library Does not match: The standard library version isn’t right for your compiler or the system you are using.
Platform-Specific Quirk: ARM64 acts in a different way than x86_64. This is because of its ABI, how it lines up memory, or how it uses registers.

Closer Look: GCC Trunk and ARM64 Details

GCC’s trunk builds are daily snapshots or nightly test builds of the compiler. These builds are used for adding new features and bug fixes before they get into stable versions. But with very new support comes problems.

Why ARM64 Is a Special Case

ARM64 (also known as AArch64) is becoming more and more common. This is true especially in mobile devices and Apple silicon devices. But it still gets less attention than x86_64 in some ways of working.

The major differences that cause problems:

Different calling conventions affecting function arguments
Stricter or more relaxed memory alignment rules
Optimizations just for this type of machine.
Conditional compilation inside the standard library

New features like std::print are not fully tested across all platforms. This is true especially for non-x86_64 ones. And this can lead to bugs that only show up on certain machine types.

📊 As more people use it, ARM64 is no longer a rare case. Canalys (2023) says ARM-based laptops make up 13.1% of global shipments. This is a rise that compiler teams should pay attention to.

Standard Library Implementations Having Problems

The C++ toolchain includes not only the compiler but also a standard library implementation. For GCC, this normally means libstdc++.

The segfaulting behavior seems to come from these things:

Not matching std::formatter<std::string> setup.
Wrongly formed internal calls to variadic format functions.
Register mismatches for variadic argument passing on ARM64.

In GCC trunk builds, the trunk compiler might be used with a standard library version that doesn't work well with it or is still being worked on.

Compiler Behavior: Pros and Cons of Trunk Builds

Using trunk builds of GCC has its benefits. You get early access to features and fixes to known bugs. And you get the chance to give feedback. But the downsides include:

Partial Support: Features like std::print might not be fully ready.
Toolchain Not Checked: There’s no way to be sure that the trunk library matches the trunk compiler.
Lack of Documentation: New bugs appear faster than they’re documented.

Simply put, trunk environments offer developers an early look at tools that are coming. But they need care and active help with testing and reporting bugs to the community.

A Story of Platforms: Differences Across Compilers

To show how random this issue can be, here’s a table of tests from user reports and tests to make the bug happen again:

Compiler	Platform	`std::print(s)` Works?	Observations
GCC trunk	ARM64	❌ Segfault	Formatter mishandled on ARM64 target
GCC 13 stable	ARM64	✅ Yes	Stable release well tested
Clang 16	x86_64	✅ Yes	Clang-based LLVM infrastructure robust
GCC 13.2 stable	x86_64	✅ Yes	No issues observed across the board
GCC trunk	x86_64	✅ Yes (mostly)	Works but subject to change

This shows the issue is strongly linked to both the machine type and the compiler version.

Solutions and Workarounds

Compiler fixes are not yet here. But several ways can help developers stop segfaults without giving up on new C++:

🔁 Use `.c_str()` as a Workaround

Most trunk failures happen because the right std::formatter overload is not found. Converting to const char* avoids this:

std::print("{}\n", s.c_str());  // Avoids formatter resolution

This gets around formatting problems. It does this by making the data look a way the compiler cannot get wrong.

🚧 Fallback to `std::cout` + `std::format`

This isn’t perfect, but it’s much more stable on builds that have problems:

std::cout << std::format("{}\n", s);  // Same output, better stability

✍️ Report the Bug

Don’t think others will fix it. Instead, be quick to report a small example that shows the bug:

Use [g++ --version] to show your compiler version.
Write down the type of machine using uname -m (look for aarch64).
Provide as few lines of code as necessary.
Share full output and stack trace (when using e.g., gdb).

Once reported, you can watch the bug’s progress and help by giving your thoughts.

Work Improvements: Ways to Stop Problems

Programming to stop compiler bugs includes:

✅ Choose stable builds instead of test trunk versions. This is true especially for code used for business.
🛠️ Use AddressSanitizer, Valgrind, or UBSan regularly.
🔍 Enable all compiler warnings (-Wall -Wextra -pedantic).
🧪 Run CI pipelines across multiple platforms (e.g., GitHub Actions with Ubuntu ARM and x86 runners).

This way of doing many things greatly lowers your chance of seeing hidden compiler bugs.

Trust, Testing, and the Compiler Ecosystem

Every time a compiler makes valid code crash, trust gets less. Developers need correct reading and running of programs that follow the rules. C++’s complicated past makes this extra important.

A feature like std::print is meant to make output simpler. But when it causes crashes when it runs, questions come up:

Did developers do something wrong?
Is C++23 truly stable?
Do trunk builds offer value or just risk?

The truth is this: compilers get made quickly, and small, unusual errors show up. Full testing by the community makes sure what the rules say matches real-world safety.

Conclusion: The Lesson Behind the Crash

This isn’t just a story about one segfault. It shows how easily modern tools can break across different machine types. Here’s what we learned:

Even safe C++23 features can fail due to tooling mismatches.
ARM64 brings in small differences compilers need to handle.
Trunk compilers are useful, but can cause problems.
Programming to stop problems and community involvement are our best tools.

Developers using new standards must find a balance between new ideas and careful work. Test widely, check your ideas, and report unusual things. That’s how we move the language—and its implementations—forward.

It can be boring to watch GCC’s and Clang’s bug trackers, mailing lists, and release notes. But it’s the best way to know about crashing bugs before they happen. Share your findings on developer forums, GitHub issues, and with your team.

Languages that change a lot may come out faster. But C++ does well because it is correct and powerful. With features like std::print, C++ is becoming clearer and easier to use. But this only happens if we make sure the tools are very good.