CODEWITHSUNDEEP
c++
Angus Comber
Angus Comber

Reputation: 9708

How to create an array of binary literals

I want an array of binary messages in my code as literals. The messages are quite smal so I thought it would be easiest to use 'binary' literals. But how to do it?

I tried this code:

struct binary_message
{
    binary_message(int size, unsigned char* bytes) : size_(size), bytes_(bytes) {}
    int size_;
    unsigned char* bytes_;
};

binary_message messages[] = {
    { 3, { 0x1, 0x2, 0x3 } },
    { 2, { 0x1, 0x2 } },
    { 1, { 0x1 } }
};

with the Visual Studio 2013 C++ compiler I get error:

error C2440: 'initializing' : cannot convert from 'initializer-list' to 'binary_message'. No constructor could take the source type, or constructor overload resolution was ambiguous

With g++ I get:

>g++ main.cpp
main.cpp:13:1: warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x [enabled by default]
main.cpp:13:1: warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x [enabled by default]
main.cpp:13:1: warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x [enabled by default]
main.cpp:13:1: error: could not convert '{3, {1, 2, 3}}' from '<brace-enclosed initializer list>' to 'binary_message'
main.cpp:13:1: error: could not convert '{2, {1, 2}}' from '<brace-enclosed initializer list>' to 'binary_message'
main.cpp:13:1: error: invalid conversion from 'int' to 'unsigned char*' [-fpermissive]
main.cpp:4:2: error:   initializing argument 2 of 'binary_message::binary_message(int, unsigned char*)' [-fpermissive]

if I use g++ -std=c++0x main.cpp I still get:

main.cpp:13:1: error: could not convert '{3, {1, 2, 3}}' from '<brace-enclosed initializer list>' to 'binary_message'
main.cpp:13:1: error: could not convert '{2, {1, 2}}' from '<brace-enclosed initializer list>' to 'binary_message'
main.cpp:13:1: error: invalid conversion from 'int' to 'unsigned char*' [-fpermissive]
main.cpp:4:2: error:   initializing argument 2 of 'binary_message::binary_message(int, unsigned char*)' [-fpermissive]

How do I fix this?

UPDATE

I guess you mean something like this?

#include <vector>
#include <iostream>

struct binary_message
{
    binary_message(std::initializer_list<unsigned char> data) : bytes_(data) {}
    std::vector<unsigned char> bytes_;
};

int main()
{
    binary_message messages[] = {
            { 0x1, 0x2, 0x3 },
            { 0x1, 0x2 },
            { 0x1 }
    };

    binary_message msg1 = messages[0];

    return 0;
}

Upvotes: 1

Views: 661

Answers (1)

SergeyA
SergeyA

Reputation: 62573

You need an initializer-list constructor if you want to use initializer lists to construct your object. Your current constructor accepts size of buffer and the buffer, but { 3, { 0x1, 0x2, 0x3 } } is nothing like that - it is an initializer list of a number and initializer list.

To properly use initializer lists, your class and constructor should be looking approximately following:

binary_message( std::initializer_list<int> data) : data(data) {}
...
std::vector<int> data;

And you would not use size at all - the size of vector would tell you.

Upvotes: 1

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