读取包含无符号整数的文件，并将其写入C ++中的二进制文件

Question

I have a text file containing unsigned integers in the range 0,..,2^32-1. Each line contains a single integer (and a newline char).

I want to write it into a binary file to save space (such that each int will take exactly 4 bytes). What'd be the best way to do that?

I've tried a few options, none of them seems to work. Help will be appreciated.

Current (non working) code:

#include <fstream>
#include <iostream>
#include <stdio.h>

int main(){
    int x;
    while (std::cin >> x){
        fwrite((void*)&x, sizeof(x), 1, stdout);
    }
    return 0;
}

It is compiled using: g++ compress.cc -o compress .

However, it seems to only output the first integer.

For example, have the I ran the command ./compress < bla | wc -c ./compress < bla | wc -c

Where "bla" is a file containing

1864754174
2150244390
1703231727

The result of the command was 4 , and not 12 as I expected.

Answer 1

your problem is that you are trying to write int instead of unsigned int. the diffrence between those 2 isnt the size of them but the use of the bytes.

in unsigned int every bit reprsent 2^(index -1) index starting from 1.

in int the bits are used like unsiged int just the last bit is used to reprsent the sign of the number and beacuse of that you can represent smaller numbers.

Answer 2

If I understood you correctly, you want to read from a text file containing uints and write those into a binary file. Reading:

std::vector<unsigned int> readUints(const std::string& filepath){
    std::vector<unsigned int> numbers;
    std::ifstream file(filepath);
    if(!file.is_open()){
        //Handle file not found
    }
    unsigned int number = 0;
    while(file >> number){
        numbers.push_back(number);
    }
    return numbers;

Writing:

void writeUints(const std::vector<unsigned int>& numbers, const std::string& filepath){
    std::ofstream file(filepath, ios_base::binary | ios_base::out);
    if(!file.is_open()){
        //Handle file not found
    }
    for(int i = 0; i < numbers.size(); i++){
        file.write(reinterpret_cast<char*>(&numbers[i], 4);
    }
}

Make sure to include <fstream> . You can change unsigned int to uint32_t to make sure it is exactly 32 bits wide on every platform