Troubleshooting and resolution of program operation problems: an instance of 'std:: Logic_ error‘what(): basic_ string::_ M_ construct null not valid

Report errors ：

terminate called after throwing an instance of 'std::logic_error'what():  basic_string::_M_construct null not valid

        java Program call jni Interface running service , Access will crash ,idea Report a mistake as above , There is no response in the browser , And it is a cross domain error （ This is caused by the failure to request a service stop ）. Many attempts failed , Check the problems one by one .

         Check java Programs and interfaces , There is no mistake , Then check jni Layer code , Note out jni call c++ Layer interface , Found that there are still problems , Then the problem should be jni layer . Further step-by-step investigation found that jstring Problems in the parameter parsing process .

solve the problem ：

         Because of the need to , Into jstring Parameters , Parameters can be empty and have data content , Parameter in jni Layer resolution to string Pass in C Code , stay C Judgment processing in code . The parameter designed here is null, and the incoming form can be info=null; perhaps info=“”; For this reason, it is passed in “” After that, the program cannot run because of the above error .

jni Used in layers jstring2string Function is ：

string jstring2string(JNIEnv *env, jstring jstr)// if jstr by “” Times wrong 
{
	char* rtn = NULL;
	jclass clsstring = env->FindClass("java/lang/String");
	jstring strencode = env->NewStringUTF("GB2312");
	jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");
	jbyteArray barr = (jbyteArray) env->CallObjectMethod(jstr, mid, strencode);
	jsize alen = env->GetArrayLength(barr);
	jbyte* ba = env->GetByteArrayElements(barr, JNI_FALSE);
	if(alen>0)
	{
		rtn = (char*)malloc(alen + 1);
		memcpy(rtn, ba, alen);
		rtn[alen] = 0;
	}
	env->ReleaseByteArrayElements(barr,ba,0);
	string stemp(rtn);
	free(rtn);
	return stemp;
}

         It is not difficult to find the reason ： Called jstring2string function , Pass in null value "",alen=0, Unprocessed but directly released the related memory , Bad memory is also returned , It will lead to abnormal memory error .

Need to take into account jstr=“” The situation of , Modification code has ：

string jstring2string(JNIEnv *env, jstring jstr)
{
	char* rtn = NULL;
	jclass clsstring = env->FindClass("java/lang/String");
	jstring strencode = env->NewStringUTF("GB2312");
	jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");
	jbyteArray barr = (jbyteArray) env->CallObjectMethod(jstr, mid, strencode);
	jsize alen = env->GetArrayLength(barr);
	jbyte* ba = env->GetByteArrayElements(barr, JNI_FALSE);
	if(alen>0)
	{
		rtn = (char*)malloc(alen + 1);
		memcpy(rtn, ba, alen);
		rtn[alen] = 0;
	}
    else
    {
        env->ReleaseByteArrayElements(barr,ba,0);
        return "";
    }
	env->ReleaseByteArrayElements(barr,ba,0);
	string stemp(rtn);
	free(rtn);
	return stemp;
}

         After modification, the program test can run normally without error , Then the problem is solved .