MinGW编译Qt项目时出现OpenSSL函数未定义引用错误求助

在Qt 5.15.2 + MinGW 7.3.0 + OpenSSL 1.1.1环境下构建项目时，编译出现大量OpenSSL函数未定义引用错误，错误信息如下：

undefined reference to `EC_KEY_free'
undefined reference to `EC_POINT_free'
undefined reference to `EC_KEY_free'
undefined reference to `EC_KEY_free'
undefined reference to `EC_POINT_free'
undefined reference to `BIO_s_mem'
undefined reference to `BIO_new'
undefined reference to `EC_GROUP_new_by_curve_name'
undefined reference to `PEM_write_bio_ECPrivateKey'
undefined reference to `PEM_write_bio_ECPKParameters'
undefined reference to `PEM_write_bio_EC_PUBKEY'
undefined reference to `BIO_read'
undefined reference to `BIO_free_all'
undefined reference to `EC_GROUP_free'
undefined reference to `EC_KEY_free'
undefined reference to `EC_KEY_new'
undefined reference to `EC_GROUP_new_by_curve_name'
undefined reference to `EC_KEY_set_group'

项目的.pro文件内容：

QT       += core gui
QT       += network widgets

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

win32:CONFIG(release, debug|release): LIBS += -L"C:/OpenSSL-Win32/lib/MinGW/libssl.a"
win32:CONFIG(release, debug|release): LIBS += -L"C:/OpenSSL-Win32/lib/MinGW/libcrypto.a"
win32: LIBS += -lgdi32 -lws2_32 -ladvapi32 -lcrypt32 -luser32

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/../dependencies/decentralised_p2p/src/release/ -ldecentralised_p2p
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/../dependencies/decentralised_p2p/build-decentralised_p2p-Desktop_Qt_5_8_0_MSVC2013_64bit2-Debug/debug/ -ldecentralised_p2p
else:macx: LIBS += -L$$PWD/../dependencies/decentralised_p2p/build-decentralised_p2p-Desktop_Qt_5_8_0_clang_64bit-Debug  -ldecentralised_p2p
else:unix: LIBS += -L$$PWD/../dependencies/decentralised_p2p/build-decentralised_p2p-Desktop-Debug/ -ldecentralised_p2p

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/../dependencies/decentralised_data/src/release/ -ldecentralised_data
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/../dependencies/decentralised_data/build-decentralised_data-Desktop_Qt_5_8_0_MSVC2013_64bit2-Debug/debug/ -ldecentralised_data
else:unix: LIBS += -L$$PWD/../dependencies/decentralised_data/build-decentralised_data-build-decentralised_p2p-Desktop-Debug-Debug/ -ldecentralised_data

win32:CONFIG(release, debug|release): LIBS += -L$$PWD/../dependencies/decentralised_crypt/src/release/ -ldecentralised_crypt
else:win32:CONFIG(debug, debug|release): LIBS += -L$$PWD/../dependencies/decentralised_crypt/build-decentralised_crypt-Desktop_Qt_5_8_0_MSVC2013_64bit2-Debug/debug/ -ldecentralised_crypt
else:unix: LIBS += -L$$PWD/../dependencies/decentralised_crypt/build-decentralised_crypt-build-decentralised_p2p-Desktop-Debug-Debug/ -ldecentralised_crypt

INCLUDEPATH += $$PWD/../dependencies/decentralised_p2p/src
DEPENDPATH += $$PWD/../dependencies/decentralised_p2p/src/release

INCLUDEPATH += $$PWD/../dependencies/decentralised_data/src
DEPENDPATH += $$PWD/../dependencies/decentralised_data/src/release

INCLUDEPATH += $$PWD/../dependencies/decentralised_crypt/src
DEPENDPATH += $$PWD/../dependencies/decentralised_crypt/src/release

win32: DEFINES += WINDOWS
macx: DEFINES += MACOSX

win32:INCLUDEPATH += "C:/OpenSSL-Win32/include/"

TARGET = decentralised_ui
TEMPLATE = app

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked as deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS
CONFIG += static
# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0


SOURCES += main.cpp\
        mainwindow.cpp \
    logindialog.cpp \
    aboutdialog.cpp \
    preferencesdialog.cpp \
    settings.cpp \
    newuserdialog.cpp

HEADERS  += mainwindow.h \
    logindialog.h \
    aboutdialog.h \
    preferencesdialog.h \
    settings.h \
    newuserdialog.h

FORMS    += mainwindow.ui \
    logindialog.ui \
    aboutdialog.ui \
    preferencesdialog.ui \
    newuserdialog.ui

RC_FILE = dc.rc

DISTFILES += \
    dc.rc

RESOURCES += \
    resources.qrc

TRANSLATIONS    = decentralised_pt.ts \
                  decentralised_ru.ts \
                  decentralised_de.ts

1. 修正OpenSSL库链接语法错误 #

.pro文件中OpenSSL的链接写法有误：-L参数用于指定库文件所在路径，而非直接指定库文件。正确写法是先指定路径，再通过-l参数指定库名（libssl.a对应-lssl，libcrypto.a对应-lcrypto）。

将原代码中的：

win32:CONFIG(release, debug|release): LIBS += -L"C:/OpenSSL-Win32/lib/MinGW/libssl.a"
win32:CONFIG(release, debug|release): LIBS += -L"C:/OpenSSL-Win32/lib/MinGW/libcrypto.a"

替换为：

win32: LIBS += -L"C:/OpenSSL-Win32/lib/MinGW" -lssl -lcrypto

2. 确保Debug模式也链接OpenSSL库 #

原配置仅在Release模式下添加了OpenSSL库链接，Debug模式未配置，导致Debug编译时找不到函数实现。上述修改后，win32: LIBS会同时作用于Debug和Release模式，解决此问题。

3. 验证库与编译器的位数匹配 #

确认你使用的OpenSSL库（C:/OpenSSL-Win32是32位版本）与MinGW编译器位数一致：若MinGW是64位，需替换为64位OpenSSL库，否则会因位数不匹配导致链接错误。

4. 检查依赖库的链接顺序 #

OpenSSL的libssl依赖libcrypto，链接时需将-lssl放在-lcrypto之前（链接器按从左到右顺序解析依赖），上述修改已遵循此顺序。

完成修改后，重新执行qmake并编译项目，即可解决未定义引用错误。

内容的提问来源于stack exchange，提问作者Ed Vestorn