ifstream.read() does not read anything?

I got some file-reading problems in my project, so I wrote following test codes.

I'm tring to read a file by ifstream.read()，but anything has been read.

I've searched numerous related questions, but still can't figure out why my code doesn't work. please help.

#include <iostream>
#include <fstream>

int main() {
    /*--------------- write file ----------------*/
    std::ofstream ofs("testfile", std::ios::binary);
    const char *content = "11223344";
    ofs.write(content, sizeof content);

    system("chmod 777 testfile");

    /*--------------- read file ----------------*/

    char arr[8] = {0};
    const int length = sizeof arr / sizeof arr[0];
    std::ifstream ifs("testfile", std::ios::binary);

    std::cout << "good: " << ifs.good() << std::endl;  // 1

    ifs.seekg(0, ifs.end);
    int file_size = ifs.tellg();
    ifs.seekg(0, ifs.beg);
    std::cout << "file_size: " << file_size << std::endl << std::endl;  // 0

    if (ifs) {
        ifs.read(&arr[0], 2);
        std::cout << "after read," << std::endl;
        std::cout << "gcount: " << ifs.gcount() << std::endl;  // 0
        std::cout << "good: " << ifs.good() << std::endl;  // 0
        ifs.read(&arr[2], 2);
        ifs.read(&arr[4], 2);
        ifs.read(&arr[6], 2);
    } else {
        std::cout << "file not found" << std::endl;
    }

    for (int i = 0; i < length; ++i) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

The output is

good: 1
file_size: 0
after read,
gcount: 0
good: 0
0 0 0 0 0 0 0 0 

This is because the data is not written to the disk. After having called ofs.write, either ofs.flush() or ofs.close() should be called to ensure data is written on disk before reading it.

Also, sizeof content to obtain the length of the string starting at address given by content pointer works, on 64 bits platforms, for this particular case where the string has 8 characters, but it will not work on other cases. The right idiom is to declare an array of characters initializing it with the literal string, then sizeof gives the size of the array which contains the terminating nul character, so to obtain the length of the string then 1 should be subtracted.

So the beginning would rather be:

/*--------------- write file ----------------*/  
std::ofstream ofs("testfile", std::ios::binary); 
const char content[] = "11223344";               
ofs.write(content, sizeof content - 1);          
ofs.close();