String of Bytes to Byte array c++

Question

Im trying to make function that takes this pattern string :

"07 C5 8F E1 FD CA 8C E2 D4 FD BC E5 03 C6 8F E2"

to return this BYTE array

BYTE pattern[] = { 0x07, 0xC5, 0x8F, 0xE1, 0xFD, 0xCA, 0x8C, 0xE2, 0xD4, 0xFD, 0xBC, 0xE5, 0x03,  0xC6, 0x8F, 0xE2};

What i tried:

BYTE strPatternToByte(std::string pattern, int len)
{
    std::vector<std::string> tokens;
    std::string token;
    std::istringstream tokenStream(pattern);
    while(std::getline(tokenStream, token, ' '))
    {
        tokens.push_back(token);
    }
    BYTE somePtr[len];
    for ( int i=0 ; i < len ; i++)
    {
        somePtr[i] = '0x' +  tokens[i];
    }

    return somePtr;
}

but the line to convert to pattern of bytes didn't work for me,

somePtr[i] = (byte) tokens[i];

is there a way in c++ to automatically parse them into bytes or something like in java?

Another problem in your source: you are returning a pointer to a local variable, which is undefined behavior. Also, you are using non-standard extension of C++ - variable-length array. — Eugene
– Eugene, Commented Sep 16, 2020 at 15:07

Some programmer dude · Accepted Answer · 2020-09-16 14:57:52Z

4

The problem is that (byte) tokens[i] doesn't translate a string to another type, instead it asks the compiler to treat the std::string object in tokens[i] as a byte, which it isn't and can't be converted to. It's basically you telling a lie to the compiler. In fact, basically all C-type casting should be a red flag that you're doing something wrong.

One solution is to instead use the normal stream extraction operator >> to parse each space-delimited hexadecimal sequence as an unsigned integer:

std::vector<unsigned> values;
std::istringstream stream(pattern);

unsigned value;
while (stream >> std::hex >> value)
{
    values.push_back(value);
}

answered Sep 16, 2020 at 14:57

Some programmer dude

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3 Comments

J.Steve Over a year ago

This solved some of the errors, but not my main problem , it still doesn' t return as i want for some reasons..

Some programmer dude Over a year ago

@J.Steve As mentioned in another comment, the code you show returns a pointer to a local variable. But converted to BYTE. Use vectors, return the vector.

Harry Over a year ago

@Someprogrammerdude why this doesn't work if I change unsigned to uint8_t

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