用C ++读写二进制信息

Question

I'm having some trouble reading and writing binary information. I can successfully write a simple string to a text file, in this case, my file 'output.dat' contains the sentence "Hello, this is a sentence".

However, I cannot read my information back. I cannot identify the problem. I intend to change every byte of the information read from the binary file later on so returning the value as a string helps.

Thanks for any help you can provide.

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

void write(const string &input) {
    fstream output("output.dat", ios::out | ios::binary);
    if (output.is_open()) {
        output.write(input.c_str(), input.size());
        output.close();
    }
}

string read(const string &fname) {
    int size;
    char* buffer;
    fstream input(fname, ios::in | ios::binary);
    if (input.is_open()) {
        input.seekg(0, ios::end);
        size = input.tellg();
        input.seekg(0, ios::beg);
        buffer = new char[size];
        input.read(buffer, size);
        input.close();
    }
    string result(buffer);
    return result;
}

int main () {
    cout << read("output.dat") << endl;

    system("pause");

    return 0;
}

Answer 1

The bug is here.

char* buffer;
input.read(buffer, size);

You're reading to the memory that buffer is pointing to.

But where is it pointing to? The pointer buffer has never been initialized.

If you know how much space you need, an approach like this will work.

std::vector<char> buffer(size);
input.read(&buffer.front(), size);

Answer 2

I really cannot understand what is going wrong in this code, as it looks fine, and works fine with me. Nevertheless, the buffer you are allocating is missing the null terminator to mark char-string end. Just change it to this:

buffer = new char[size+1];
input.read(buffer, size);
buffer[size] = 0;