鏈接器：未定義的const C結構的引用，它位於靜態lib中

Question

我有以下問題：

頭文件“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
};

鏈接器返回未定義的引用'can_initstruct'can_filter_acceptall''can_filter_1''can_filter_2'...文件can_settings。{c，h}構建為靜態庫，用於我的主應用程序（僅限C）和我的CAN低級驅動程序（C ++）。 所有靜態庫都是在我的低級驅動程序和主應用程序構建之前構建的。 使用objdump我轉儲了靜態CAN設置庫，所有上述結構都列在.rodata部分中。 我做錯了什么......？

Answer 1

如果您正在使用GCC，請確保以正確的順序指定庫。 請參閱為什么庫鏈接的順序有時會導致GCC錯誤？ 詳細說明。

但是，如果您不想打擾庫序列，只需指定序列兩次而不是一次。 應用於上述問題的公認答案，這意味着：

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

作為替代方案，使用-Wl,--start-group ... -Wl,--end-group GCC的-Wl,--end-group標志（ GCC：什么是--start-group和--end-group命令行選項？ ） 。

Answer 2

好，我知道了。 您在GCC中指定目標文件和庫的順序非常重要！ 鏈接器搜索以它們出現的順序進行思考，因此如果您有一個包含對庫函數調用的源文件，則需要將它放在庫之前，否則鏈接器將不知道它必須解析它。 我做錯了......

謝謝你的暗示。