[#uint256-2constructor-09]
= xref:uint256.adoc[uint256]::uint256
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Constructors

== Synopses

Declared in `<uint256.h>`

Constructs a zero‐valued uint256.


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constexpr
xref:uint256/2constructor-05.adoc[uint256]() = default;
----

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Constructs a uint256 at compile time from a hex string.


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consteval
explicit
xref:uint256/2constructor-07.adoc[uint256](std::string_view hex_str);
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Constructs a uint256 from a single byte constant between 1 and 255.


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constexpr
explicit
xref:uint256/2constructor-0f.adoc[uint256](uint8_t v);
----

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Constructs a uint256 by copying bytes from a span.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
explicit
xref:uint256/2constructor-0d.adoc[uint256](std::span<unsigned char const> vch);
----

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== Parameters

[cols="1,4"]
|===
| Name| Description
| *hex_str*
| A hex string that must fit the 256‐bit blob exactly.
| *v*
| The byte value placed in the first position of the blob.
| *vch*
| A span of exactly 32 bytes to copy into the blob.
|===


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