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Overview

Opcode: 0x38 Introduced: Frontier (EVM genesis) CODESIZE pushes the byte length of the currently executing code onto the stack.

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Specification

Stack Input: 
[]
Stack Output: 
size (uint256, in bytes)
Gas Cost: 2 (GasQuickStep) Operation: 
stack.push(code.length)

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Behavior

Returns the size of the currently executing bytecode, including deployed code and constructor code.

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Examples

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Basic Usage

function getCodeSize() public pure returns (uint256 size) {
    assembly {
        size := codesize()
    }
}

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Code Copying

function copyOwnCode() public pure returns (bytes memory code) {
    assembly {
        let size := codesize()
        code := mload(0x40) // Free memory pointer
        mstore(code, size)
        codecopy(add(code, 0x20), 0, size)
        mstore(0x40, add(add(code, 0x20), size))
    }
}

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Gas Cost

Cost: 2 gas (GasQuickStep)

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Common Usage

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Constructor Detection

During contract construction, CODESIZE includes constructor code. After deployment, only runtime code.

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Implementation

export function codesize(frame: FrameType): EvmError | null {
  const gasErr = consumeGas(frame, 2n);
  if (gasErr) return gasErr;

  const pushErr = pushStack(frame, BigInt(frame.bytecode.length));
  if (pushErr) return pushErr;

  frame.pc += 1;
  return null;
}

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References