Why does solc output bytecode that is not in valid hex format?

Question

I compile my solidity file using the following command:

solc Encoder.sol --bin --abi --optimize -o <output_dir>/

Then I try to deploy it in Geth:

Encoder = eth.contract([<abi file content>])
deployEncoder = {from:eth.coinbase, data:"0x<bin file content>", gas:2000000}>}

getPartialInstanceEncoder = Encoder.new([], deployEncoder)

The last line throws an exception. Looking closer into the bin file content, I figured out that the bin file contains several invalid characters, either '$' or '_'. What is the reason for this?

I uploaded my bin file here (since it is too large for the text here), you can search for the characters in your browser: https://file.io/OIFtZM

Answer 1

Just a guess because the link seems to be dead, but maybe you're using libraries?

From https://solidity.readthedocs.io/en/v0.5.11/using-the-compiler.html:

If your contracts use libraries, you will notice that the bytecode contains substrings of the form __$53aea86b7d70b31448b230b20ae141a537$__. These are placeholders for the actual library addresses. The placeholder is a 34 character prefix of the hex encoding of the keccak256 hash of the fully qualified library name. The bytecode file will also contain lines of the form // <placeholder> -> <fq library name> at the end to help identify which libraries the placeholders represent. Note that the fully qualified library name is the path of its source file and the library name separated by :. You can use solc as a linker meaning that it will insert the library addresses for you at those points:

Either add --libraries "file.sol:Math:0x1234567890123456789012345678901234567890 file.sol:Heap:0xabCD567890123456789012345678901234567890" to your command to provide an address for each library or store the string in a file (one library per line) and run solc using --libraries fileName.