printf calling default __io_putchar instead of redefinition

[EthanMankins]

I am using the Nucleo-H743ZI with a c++ project, and have used this code many times before with this board and c++; however, now the printf() function no longer prints to uart:

int __io_putchar(int ch) {
      HAL_UART_Transmit(&huart3, (uint8_t*) &ch, 1, 0xFFFF);
      return ch;
}
[...]
printf("hello\n");

 I can send chars using HAL_UART_Transmit(&huart3, (uint8_t*) &ch, 1, 0xFFFF);

I stepped through the disassembly and found that __io_putchar is called with the following:

112       		__io_putchar(*ptr++);
08003718:   ldr     r3, [r7, #8]
0800371a:   adds    r2, r3, #1
0800371c:   str     r2, [r7, #8]
0800371e:   ldrb    r3, [r3, #0]
08003720:   mov     r0, r3
08003722:   nop.w   

To the best I can tell, it seems like the default weak __io_putchar is being called.

In the memory map file it is listed as:

 .text._Z12__io_putchari
                0x00000000       0x24 ./Core/Src/main.o

 Ant ideas what is going wrong and how to fix it?

Thanks,
Ethan

[Tesla DeLorean · Accepted solution]

Shouldn't you be using extern "C" to prevent the name mangling?

extern "C" int __io_putchar(int ch) { ...

[EthanMankins]

Could've sworn I had tried that, but that fixed it...