Strings.md

Solidity Tutorial : all about Strings

As a general rule, you should use stringfor arbitrary-length string (UTF-8) data. Strings heavily involve the use of bytes in Solidity

Strings as Arrays

In Solidity, string are actually a special type of arrays (Like abytes is similar to byte[] ).

String are actually equal to bytes but does not allow length or index access.

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String Literals

In Solidity, strings can be written with either double or single-quotes ("foo" or 'bar').

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Escape characters in String Literals

String literals support the following escape characters:

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\xNN takes a hex value and inserts the appropriate byte, while \uNNNN takes a Unicode codepoint and inserts an UTF-8 sequence.

The string in the following example has a length of ten bytes. It starts with a newline byte, followed by a double quote, a single quote a backslash character and then (without separator) the character sequence abcdef.

"\n\"\'\\abc\
def"

Any unicode line terminator which is not a newline (i.e. LF, VF, FF, CR, NEL, LS, PS) is considered to terminate the string literal. Newline only terminates the string literal if it is not preceded by a .

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Compare two strings.

You can compare two strings by their keccak256-hash using :

keccak256(abi.encodePacked(s1)) == keccak256(abi.encodePacked(s2)) .

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Concatenate two strings.

You can concatenate two strings using abi.encodePacked() method. Here is an example below.

string s1 = "Hello ";
string s2 = "World";

function concatenateStrings(string s1, string s2) internal pure returns (bytes) {
    return abi.encodePacked(s1, s2);
}

We could also do it differently. We would first need to convert the two values pass as parameters into bytes.

In other programming languages like PHP, you can reference the individual values of a string. In fact, a string is an array of integers cast to their ASCII character values.

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Data Location with Strings

Let's see how you can create a new string character by character. This will introduce us to one peculiarity of Solidity programming: data location.

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Additional notes on Strings

If you want to access the byte-representation of a string s, use bytes(s).length / bytes(s)[7] = 'x';. Keep in mind that you are accessing the low-level bytes of the UTF-8 representation, and not the individual characters.

String literals can be implicitly converted to fixed-size byte arrays, if their number of characters matches the size of the bytes type:

bytes2 b = "xy"; // fine
bytes2 e = "x"; // not allowed
bytes2 f = "xyz"; // not allowed

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## String escapes

Escape type	Description
\<newline>	escape an actual new line
\\	backslash
\'	single quote
\"	double quote
\b	backspace
\f	form feed
\n	newline
\r	carriage return
\t	tab
\v	vertical tab
\xNN	hex escape
\uNNNN	unicode escape

What you can't do with Strings in Solidity ?

• Solidity does not have string manipulation functions, but there are third-party string libraries.