c - 链接器 : Undefined Reference for const C structs which are located in static lib

Question

我有以下问题:

头文件“can_settings.h”:

#ifndef CAN_SETTINGS_H_
#define CAN_SETTINGS_H_

#ifdef __cplusplus
extern "C" {
#endif

#include "can.h"

extern const CAN_InitTypeDef can_initstruct;

extern const CAN_FilterInitTypeDef can_filter_acceptall;
extern CAN_FilterInitTypeDef can_filter_1;
extern CAN_FilterInitTypeDef can_filter_2;


#ifdef __cplusplus
}
#endif

#endif

源文件“can_settings.c”:

#include "can_settings.h"

const CAN_InitTypeDef can_initstruct = {
#ifdef SYSCLK_FREQ_72MHz
    // APB1_freq = 36 MHz
    /* .CAN_Prescaler = */ 24,
    /* .CAN_Mode = */ CAN_Mode_Normal,
    /* .CAN_SJW = */ CAN_SJW_1tq,
    /* .CAN_BS1 = */ CAN_BS1_8tq,
    /* .CAN_BS2 = */ CAN_BS2_3tq,
#elif defined SYSCLK_FREQ_24MHz
    // APB1_freq = 24 MHz
    /* .CAN_Prescaler = */ 16,
    /* .CAN_Mode = */ CAN_Mode_Normal,
    /* .CAN_SJW = */ CAN_SJW_1tq,
    /* .CAN_BS1 = */ CAN_BS1_8tq,
    /* .CAN_BS2 = */ CAN_BS2_3tq,
#endif
    /* .CAN_TTCM = */ DISABLE,
    /* .CAN_ABOM = */ DISABLE,
    /* .CAN_AWUM = */ DISABLE,
    /* .CAN_NART = */ DISABLE,
    /* .CAN_RFLM = */ DISABLE,
    /* .CAN_TXFP = */ ENABLE,
};

const CAN_FilterInitTypeDef can_filter_acceptall = {
    /* .CAN_FilterIdHigh = */ 0x0000,
    /* .CAN_FilterIdLow = */ 0x0000,
    /* .CAN_FilterMaskIdHigh = */ 0x0000,
    /* .CAN_FilterMaskIdLow = */ 0x0000,
    /* .CAN_FilterFIFOAssignment = */ 0,
    /* .CAN_FilterNumber = */ 0,
    /* .CAN_FilterMode = */ CAN_FilterMode_IdMask,
    /* .CAN_FilterScale = */ CAN_FilterScale_32bit,
    /* .CAN_FilterActivation = */ ENABLE
};

const CAN_FilterInitTypeDef can_filter_1 = {
        /* .CAN_FilterIdHigh = */ 0x0000,
        /* .CAN_FilterIdLow = */ CAN_ID_EXT,
        /* .CAN_FilterMaskIdHigh = */ 0x14FC << 3,
        /* .CAN_FilterMaskIdLow = */ CAN_ID_EXT,
        /* .CAN_FilterFIFOAssignment = */ 0,
        /* .CAN_FilterNumber = */ 0,
        /* .CAN_FilterMode = */ CAN_FilterMode_IdMask,
        /* .CAN_FilterScale = */ CAN_FilterScale_32bit,
        /* .CAN_FilterActivation = */ ENABLE
};

const CAN_FilterInitTypeDef can_filter_2 = {
        /* .CAN_FilterIdHigh = */ 0x0000,
        /* .CAN_FilterIdLow = */ CAN_ID_EXT,
        /* .CAN_FilterMaskIdHigh = */ 0x1400 << 3,
        /* .CAN_FilterMaskIdLow = */ CAN_ID_EXT,
        /* .CAN_FilterFIFOAssignment = */ 0,
        /* .CAN_FilterNumber = */ 1,
        /* .CAN_FilterMode = */ CAN_FilterMode_IdMask,
        /* .CAN_FilterScale = */ CAN_FilterScale_32bit,
        /* .CAN_FilterActivation = */ ENABLE
};

链接器返回对 'can_initstruct' can_filter_acceptall' 'can_filter_1' 'can_filter_2' 的 undefined reference ... 文件 can_settings.{c, h} 是作为静态库构建的，用于我的主应用程序(仅 C)和我的 CAN 低级驱动程序(C++)。 所有静态库都是在构建低级驱动程序和主应用程序之前构建的。 使用 objdump，我转储了静态 CAN 设置库，并且上述所有结构都按原样列在 .rodata 部分中。 我做错了什么......？

Answer 1

如果您使用的是 GCC，请确保以正确的顺序指定库。参见 Why does the order in which libraries are linked sometimes cause errors in GCC?获取详细说明。

但是，如果您不想理会库序列，只需指定序列两次，而不是一次。应用于上述问题的公认答案，这意味着:

gcc prog.o libA.a libB.a libA.a libB.a -o prog.x

作为替代方案，使用 -Wl,--start-group ... -Wl,--end-group 标志海湾合作委员会 ( GCC: what are the --start-group and --end-group command line options? )。