Use string type or bytes32?

Question

What are the benefits to using string datatypes over bytes32 to represent text data. It seems my contract runs into an out of gas exception when I switch the data structures from bytes32 to string.

Answer 1

Why string instead of bytes32?

Use string for arbitrary-length string (UTF-8) data that's longer than 32 bytes. Frontends can decode a long string easier using methods like web3.toAscii or UTF-8 (when issues are fixed), instead of implementing the logic of UTF-8 decoding a series of bytes32.

From Solidity docs:

As a rule of thumb, use bytes for arbitrary-length raw byte data and string for arbitrary-length string (UTF-8) data. If you can limit the length to a certain number of bytes, always use one of bytes1 to bytes32 because they are much cheaper.

String literals may also be helpful or convenient:

String literals are written with either double or single-quotes ("foo" or 'bar')...

String literals support escape characters, such as \n, \xNN and \uNNNN. \xNN takes a hex value and inserts the appropriate byte, while \uNNNN takes a Unicode codepoint and inserts an UTF-8 sequence.

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Why bytes32 instead of string?

Answered in Why do Solidity examples use bytes32 type instead of string?

bytes32 uses less gas because it fits in a single word of the EVM, and string is a dynamically sized-type which has current limitations in Solidity (such as can't be returned from a function to a contract).

Answer 2

Like the other post said, you only want to use strings for dynamically allocated data, otherwise Byte32 is going to perform better. Bytes32 is also going to be better in gas. If you want to play around with it, I built a little fiddle of it https://ethfiddle.com/70ipaEIFdk

Byte used 21465 gas

String used 21897 gas

pragma solidity ^0.4.18;

contract SampleOverflow {
  string constant statictext = "HelloStackOverFlow";
  bytes32 constant byteText = "HelloStackOverFlow";
  function  getString() payable public  returns(string){
    return statictext;
  }

  function  getByte() payable public returns(bytes32){
    return byteText;
  }
}

Get Byte

Get String https://ethfiddle.com/70ipaEIFdk

Answer 3

bytes32 means string with max length 32, It takes less memory than string for the same length of the string.

So, when your data is not more than 32 bytes (32 words), use bytes32.

If the length of the string is not defined, use just bytes.

also, byte8,byte16,byte32 are all available. You can use any as per conditions.