CODEWITHSUNDEEP
c++file-iobinarycertificatepng
Chris
Chris

Reputation: 3057

Load certificate and png into char*

I'm trying to load a certificate and a png file into a char* in C++:

char certPath[] = "./user.pem";
char dataPath[] = "./test.png";    
char *certificate = loadFile(certPath);
char *datafile = loadFile(dataPath);

And this is my loadFile()` method:

char* loadFile(char* filename) {
    cout << endl << "Loading file: " << filename << endl;

    char *contents;
    ifstream file(filename, ios::in|ios::binary|ios::ate);
    if (file.is_open())
    {
        int size = file.tellg();
        contents = new char [size];
        file.seekg (0, ios::beg);
        file.read (contents, size);
        file.clear();
        file.close();
    }
    printf("contents: %s\n", contents);
    cout << endl << "finished loading " << filename << endl;

    return contents;
}

This is the output which it produces:

    Loading file: ./user.pem
contents: -----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----


finished loading ./user.pem

Loading file: ./test.png

First the content of the certificate should appear and then the content of the image. The certificate works but when I try to load the image it is really strange. Nothing works anymore. Even a simple cout or printf doesn't show up on the console but the program doesn't crash...

Any suggestions what's wrong?

Upvotes: 1

Views: 911

Answers (3)

Fabio Ceconello
Fabio Ceconello

Reputation: 16049

You can't print the contents of a png file to the console, it's a binary file - different from a certificate file, which contains the certificate MIME-encoded and thus is a regular text file.

A printable file (i.e. text) contains only bytes representing standard-ASCII characters (0x20 - 0x7F) and uses ASCII formatting characters (CR, LF, etc.) in a predictable way. Furthermore, it doesn't contain a 0x00 byte, which is used in C/C++ to mark the end of a string. A binary file may contain any byte in any order.

So, two things will happen when you try to print it: a) it'll stop at the first 0x00 byte found; b) every byte containing a non-ASCII character will be printed as a special char (if it's in the code page active for the console), or nothing at all, and bytes that contain ASCII formatting chars will be "executed" as if they were actual formatting in a text file.

The result: either you won't see anything at all or just a few strange chars mixed with random line feeds, tabs & etc.

To have what you expect, the first thing is to define exactly what it is. Do you want to see the png contents MIME-encoded? Then you should use a MIME-encoding routine (like this). Or do you want to print the hex value of each byte? Then you need to do std::cout << std::hex << byte (as Nawaz suggested) or printf("%02x") for each byte in a loop.

Also for the certificate file you should open as a text file, not binary. Otherwise, you'd have two undesired effects: no LF normalization (for instance, in Windows the EOL is marked by CR+LF, while in Unix/Linux it's just LF) and no handling for the EOF char.

Upvotes: 1

Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361612

There are different kinds of PNG file. So it could be the PNG image is having non-printable character. If so, then it will not be printed using any print function, be it printf or std::cout<<.

However, you can print the hexadecimal values of non-printable character:

//write it inside the if-block
for(int i = 0 ; i < size; ++i)
      std::cout << std::hex << (int) contents[i];

It would print hexadecimal value of each character.

You can test if a given character is printable or not, using isprint() function.

Upvotes: 2

Ylisar
Ylisar

Reputation: 4291

Your error is that you have \0 at the beginning of the PNG header.

EDIT:

Change:

printf("contents: %s\n", contents);

To:

std::cout.write( contents, size );
std::cout.flush();

You have to move size into the correct scope as well of course.

Upvotes: 2

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