Atmel Studio：对“_read”的未定义引用

Question

I started receiving the following Linker error with Atmel Studio:

c:/program files (x86)/atmel/studio/7.0/toolchain/arm/arm-gnu-toolchain/bin/../lib/gcc/arm-none-eabi/6.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m\libc.a(lib_a-readr.o): 
In function `_read_r':
    C:\Users\Administrator\Documents\myproj\Debug\readr.c(1,1): error: undefined reference to `_read'

This happened after I added a virtual method to my project. What is going on?

Answer 1

Answer originally pulled from this site .

What's going on is that a built-in __cxa_pure_virtual defaults to using _read and _write via printf . To fix, explicitly define that handler to do something else.

extern "C" void __cxa_pure_virtual();
extern "C" void __cxa_pure_virtual() { 
    // Add custom handler here
    while(1); 
}

Answer 2

In my case, I traced it to an issue with the asf defining assert() to something invalid when 'NDEBUG' is not defined in the project compile\\link symbols.

Specifically,

• Project properties->Toolchain->ARM\\GNU C Compiler->Symbols: Add NDEBUG as a -D 'defined symbol'.
• Project properties->Toolchain->ARM\\GNU Preprocessing Assembler->Symbols: Add NDEBUG as a -D 'defined symbol'.

Answer 3

In my case, this issue was related to the linker settings of the project configuration.

By setting the linker settings "Additional Specs" to " Use syscall stubs (--specs=nosys.specs) ", empty syscall implementations for posix system calls like read and write are provided.

These settings are located under

Project Properties -> Toolchain -> ARM/GNU Linker -> General -> Additional Specs