Question

我引用了另一个stackoverflow文章“如何将指针映射到JNA中的结构数组”，以提供以下代码来枚举Windows服务依赖项。

结构和功能声明：

static class SERVICE_STATUS extends Structure {
    public int dwServiceType;
    public int dwCurrentState;
    public int dwControlsAccepted;
    public int dwWin32ExitCode;
    public int dwServiceSpecificExitCode;
    public int dwCheckPoint;
    public int dwWaitHint;
    public SERVICE_STATUS(){}
}

static class ENUM_SERVICE_STATUS extends Structure {
    public ENUM_SERVICE_STATUS(){ }

    public WString lpServiceName;
    public WString lpDisplayName;
    SERVICE_STATUS serviceStatus;
}

boolean EnumDependentServicesW(Pointer hService, int serviceState, ENUM_SERVICE_STATUS serviceStatuses, int size, IntByReference bytesNeeded, IntByReference servicesReturned);

如果只有一个服务依赖项，则以下代码有效：

IntByReference bytesNeeded = new IntByReference();
IntByReference numberOfServices = new IntByReference();
Advapi32.ENUM_SERVICE_STATUS serviceStatus = new Advapi32.ENUM_SERVICE_STATUS();
Advapi32.ENUM_SERVICE_STATUS[] serviceStatuses = (Advapi32.ENUM_SERVICE_STATUS[]) serviceStatus.toArray(1);

if (!advapi32.EnumDependentServicesW(serviceHandle, Advapi32.SERVICE_ACTIVE, null, 0, bytesNeeded, numberOfServices)) {
    if (advapi32.EnumDependentServicesW (serviceHandle, Advapi32.SERVICE_ACTIVE, serviceStatuses[0], bytesNeeded.getValue(), bytesNeeded, numberOfServices)) {
        for(int i = numberOfServices.getValue() - 1; i >= 0; i--){
            logger.debug("Service Name: " + serviceStatuses[i].lpServiceName.toString());
    }
}

如果有2个服务依赖项，我在logger.debug调用中得到lpServiceName的NullPointerException：

IntByReference bytesNeeded = new IntByReference();
IntByReference numberOfServices = new IntByReference();
Advapi32.ENUM_SERVICE_STATUS serviceStatus = new Advapi32.ENUM_SERVICE_STATUS();
Advapi32.ENUM_SERVICE_STATUS[] serviceStatuses = (Advapi32.ENUM_SERVICE_STATUS[]) serviceStatus.toArray(2);

if (!advapi32.EnumDependentServicesW(serviceHandle, Advapi32.SERVICE_ACTIVE, null, 0, bytesNeeded, numberOfServices)) { 
    if (advapi32.EnumDependentServicesW (serviceHandle, Advapi32.SERVICE_ACTIVE, serviceStatuses[0], bytesNeeded.getValue(), bytesNeeded, numberOfServices)) {
        for(int i = numberOfServices.getValue() - 1; i >= 0; i--){
            logger.debug("Service Name: " + serviceStatuses[i].lpServiceName.toString());
    }
}

正如预期的那样，上面代码的numberOfServices值为2。我试图传递结构数组而不是指针，因为我希望JNA进行内存同步。我应该如何传递/使用结构数组？

Answer 1

根据EnumDependentServices的{{3}}，

lpServices [out，optional]


指向数组的指针     接收名称和服务的ENUM_SERVICE_STATUS结构     数据库中每个依赖服务的状态信息。的 的     缓冲区必须足够大以容纳结构和字符串     他们的成员指出的。

您几乎忽略了bytesNeeded报告的所需缓冲区大小。您应该使用bytesNeeded值创建必需大小的Memory实例，然后使用该Memory实例创建新的ENUM_SERVICE_STATUS实例，而不是独立创建结构所需的缓冲区大小。

如何使用JNA传递结构数组

1 个答案: