native-calls.cpp

#include <jni.h>
#include <string>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <iostream>
#include <string.h>
#include <android/log.h>

#define BLOCK_SIZE 4096

extern "C"
JNIEXPORT jstring

JNICALL
Java_edu_ufl_cise_os_p2_P2Activity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

/*
 * This is the new function readFile i added to implement the natuve file reading functionality
 */

extern "C"
JNIEXPORT jstring JNICALL Java_edu_ufl_cise_os_p2_P2Activity_readFile(
        JNIEnv *env,
        jobject, jstring path) {

    char * _path = (char *) env->GetStringUTFChars(path, NULL);
    __android_log_print(ANDROID_LOG_VERBOSE, "readFile", "%s", _path);
    int fd = -1;
    ssize_t bytes_read = -1;
//    POSIX commnad to open the file
    fd = open((const char *) _path, O_RDONLY);
    if (fd == -1) {
        __android_log_print(ANDROID_LOG_VERBOSE, "readFile", "error in opening file");
    }

//    seeking file to get the size of file and allocating the buffer of size of file
    off_t sizeOfFile = lseek(fd, 0 , SEEK_END);
    lseek(fd, 0,SEEK_SET);
    char* buff = new char[sizeOfFile];
//    adding null character at the end of buffer
    buff[sizeOfFile] = '\0';
//    using POSIX read() command to read files
    while ((bytes_read = read(fd, buff, BLOCK_SIZE)) > 0);
    jstring thisRead = env->NewStringUTF(buff);
//    dealocating the memory
    delete[] buff;
    return thisRead;
}