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<!DOCTYPE html>
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<title>Go strconv Package — Ultimate Guide</title>
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</head>
<body>
<div class="hero">
<h1>Go <span>strconv</span> Package</h1>
<p>Convert between strings and numbers, booleans, and quoted representations — the bridge between text and typed values.</p>
<div class="hero-pills">
<span>Atoi / Itoa</span>
<span>ParseInt / FormatInt</span>
<span>ParseFloat / FormatFloat</span>
<span>ParseBool / FormatBool</span>
<span>Quote / Unquote</span>
<span>AppendInt</span>
</div>
</div>
<div class="layout">
<nav class="pkg-nav">
<a href="index.html" class="home-link">Go Handbook</a>
<div class="nav-group">Language</div>
<ul class="pkg-list">
<li><a href="basics.html"><span class="pkg-icon">📖</span>Basics</a></li>
<li><a href="data-structures.html"><span class="pkg-icon">📦</span>Data Structures</a></li>
<li><a href="concurrency.html"><span class="pkg-icon">🔀</span>Concurrency</a></li>
<li><a href="testing.html"><span class="pkg-icon">🧪</span>Testing</a></li>
<li><a href="reflection.html"><span class="pkg-icon">🔬</span>Reflection</a></li>
<li><a href="file-data.html"><span class="pkg-icon">📁</span>File & Data</a></li>
<li><a href="web.html"><span class="pkg-icon">🌐</span>Web</a></li>
<li><a href="packages-modules.html"><span class="pkg-icon">🗃</span>Packages & Modules</a></li>
<li><a href="performance.html"><span class="pkg-icon">⚡</span>Performance</a></li>
<li><a href="gotchas.html"><span class="pkg-icon">⚠️</span>Gotchas</a></li>
</ul>
<div class="nav-group">Packages</div>
<ul class="pkg-list">
<li><a href="strings-package-guide.html"><span class="pkg-icon">🔤</span>strings</a></li>
<li><a href="fmt-package-guide.html"><span class="pkg-icon">🖨</span>fmt</a></li>
<li><a href="strconv-package-guide.html" class="active"><span class="pkg-icon">🔢</span>strconv</a></li>
<li><a href="sort-package-guide.html"><span class="pkg-icon">📊</span>sort</a></li>
<li><a href="slices-package-guide.html"><span class="pkg-icon">🗂</span>slices</a></li>
<li><a href="io-package-guide.html"><span class="pkg-icon">🔌</span>io</a></li>
<li><a href="os-package-guide.html"><span class="pkg-icon">💻</span>os</a></li>
<li><a href="errors-package-guide.html"><span class="pkg-icon">⚠️</span>errors</a></li>
<li><a href="context-package-guide.html"><span class="pkg-icon">🎯</span>context</a></li>
<li><a href="time-package-guide.html"><span class="pkg-icon">⏱</span>time</a></li>
<li><a href="math-package-guide.html"><span class="pkg-icon">🧮</span>math</a></li>
</ul>
</nav>
<main class="content">
<!-- ── 1. ATOI / ITOA ────────────────────────────────── -->
<section class="section" id="atoi-itoa">
<div class="section-header">
<div class="section-icon icon-blue">🔁</div>
<h2>Atoi & Itoa</h2>
<span class="section-tag">int ↔ string shortcut</span>
</div>
<div class="callout tip">
<span class="callout-icon">💡</span>
<div><code>Atoi</code> and <code>Itoa</code> are convenience wrappers around <code>ParseInt</code> and <code>FormatInt</code> for the common case of base-10 <code>int</code>. Use them when you just need a quick int/string round-trip.</div>
</div>
<div class="two-col">
<div class="card">
<div class="card-header">
<span class="card-title">Atoi — string to int</span>
<span class="card-badge badge-blue">Atoi</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// Atoi — "ASCII to integer"</span>
n, err := <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(<span class="str">"42"</span>)
<span class="cmt">// n=42, err=nil</span>
n, err = <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(<span class="str">"-17"</span>)
<span class="cmt">// n=-17, err=nil</span>
n, err = <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(<span class="str">"abc"</span>)
<span class="cmt">// n=0, err=*NumError</span>
<span class="cmt">// Typical use: parsing CLI args or env vars</span>
port, err := <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(<span class="pkg">os</span>.<span class="fn">Getenv</span>(<span class="str">"PORT"</span>))
<span class="kw">if</span> err != <span class="kw">nil</span> {
port = <span class="num">8080</span>
}</pre>
</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">Itoa — int to string</span>
<span class="card-badge badge-blue">Itoa</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// Itoa — "integer to ASCII"</span>
s := <span class="pkg">strconv</span>.<span class="fn">Itoa</span>(<span class="num">42</span>) <span class="cmt">// "42"</span>
s = <span class="pkg">strconv</span>.<span class="fn">Itoa</span>(-<span class="num">17</span>) <span class="cmt">// "-17"</span>
s = <span class="pkg">strconv</span>.<span class="fn">Itoa</span>(<span class="num">0</span>) <span class="cmt">// "0"</span>
<span class="cmt">// Common uses</span>
id := <span class="pkg">strconv</span>.<span class="fn">Itoa</span>(userID)
filename := <span class="str">"page-"</span> + <span class="pkg">strconv</span>.<span class="fn">Itoa</span>(pageNum) + <span class="str">".html"</span>
<span class="cmt">// Note: fmt.Sprintf("%d", n) is equivalent but slower</span>
<span class="cmt">// Itoa is the idiomatic choice for int → string</span></pre>
</div>
</div>
</div>
</section>
<!-- ── 2. PARSEINT / FORMATINT ───────────────────────── -->
<section class="section" id="integers">
<div class="section-header">
<div class="section-icon icon-green">🔢</div>
<h2>Integers — Parse & Format</h2>
<span class="section-tag">ParseInt · ParseUint · FormatInt</span>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">ParseInt — parse with base and bit size</span>
<span class="card-badge badge-green">ParseInt</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// ParseInt(s, base, bitSize) → int64, error</span>
<span class="cmt">// base: 0 (detect from prefix), 2–36; bitSize: 0,8,16,32,64</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"42"</span>, <span class="num">10</span>, <span class="num">64</span>) <span class="cmt">// 42, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"-42"</span>, <span class="num">10</span>, <span class="num">64</span>) <span class="cmt">// -42, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"ff"</span>, <span class="num">16</span>, <span class="num">64</span>) <span class="cmt">// 255, nil — hex</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"111"</span>, <span class="num">2</span>, <span class="num">64</span>) <span class="cmt">// 7, nil — binary</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"17"</span>, <span class="num">8</span>, <span class="num">64</span>) <span class="cmt">// 15, nil — octal</span>
<span class="cmt">// base 0 — auto-detect from prefix</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"0xff"</span>, <span class="num">0</span>, <span class="num">64</span>) <span class="cmt">// 255 — 0x prefix → hex</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"0b1010"</span>, <span class="num">0</span>, <span class="num">64</span>) <span class="cmt">// 10 — 0b prefix → binary</span>
<span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"0o17"</span>, <span class="num">0</span>, <span class="num">64</span>) <span class="cmt">// 15 — 0o prefix → octal</span>
<span class="cmt">// ParseUint — unsigned only</span>
<span class="pkg">strconv</span>.<span class="fn">ParseUint</span>(<span class="str">"255"</span>, <span class="num">10</span>, <span class="num">8</span>) <span class="cmt">// 255, nil — fits in uint8</span>
<span class="pkg">strconv</span>.<span class="fn">ParseUint</span>(<span class="str">"256"</span>, <span class="num">10</span>, <span class="num">8</span>) <span class="cmt">// 0, ErrRange — overflows uint8</span></pre>
</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">FormatInt — integer to string in any base</span>
<span class="card-badge badge-green">FormatInt</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// FormatInt(i int64, base int) → string</span>
<span class="pkg">strconv</span>.<span class="fn">FormatInt</span>(<span class="num">255</span>, <span class="num">10</span>) <span class="cmt">// "255"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatInt</span>(<span class="num">255</span>, <span class="num">16</span>) <span class="cmt">// "ff"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatInt</span>(<span class="num">255</span>, <span class="num">2</span>) <span class="cmt">// "11111111"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatInt</span>(<span class="num">255</span>, <span class="num">8</span>) <span class="cmt">// "377"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatInt</span>(-<span class="num">42</span>, <span class="num">10</span>) <span class="cmt">// "-42"</span>
<span class="cmt">// FormatUint — unsigned</span>
<span class="pkg">strconv</span>.<span class="fn">FormatUint</span>(<span class="num">255</span>, <span class="num">16</span>) <span class="cmt">// "ff"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatUint</span>(<span class="num">255</span>, <span class="num">2</span>) <span class="cmt">// "11111111"</span></pre>
</div>
</div>
</section>
<!-- ── 3. PARSEFLOAT / FORMATFLOAT ──────────────────── -->
<section class="section" id="floats">
<div class="section-header">
<div class="section-icon icon-gold">🌊</div>
<h2>Floats — Parse & Format</h2>
<span class="section-tag">ParseFloat · FormatFloat</span>
</div>
<div class="callout">
<span class="callout-icon">ℹ️</span>
<div><code>ParseFloat</code> always returns a <code>float64</code>. Pass <code>bitSize=32</code> to constrain the result to float32 range — the returned value is still <code>float64</code> but safe to cast.</div>
</div>
<div class="two-col">
<div class="card">
<div class="card-header">
<span class="card-title">ParseFloat</span>
<span class="card-badge badge-gold">ParseFloat</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// ParseFloat(s, bitSize) → float64, error</span>
<span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"3.14"</span>, <span class="num">64</span>) <span class="cmt">// 3.14, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"-2.71"</span>, <span class="num">64</span>) <span class="cmt">// -2.71, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"1.5e3"</span>, <span class="num">64</span>) <span class="cmt">// 1500, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"NaN"</span>, <span class="num">64</span>) <span class="cmt">// NaN, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"Inf"</span>, <span class="num">64</span>) <span class="cmt">// +Inf, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"abc"</span>, <span class="num">64</span>) <span class="cmt">// 0, ErrSyntax</span>
<span class="cmt">// Parse as float32 precision</span>
v, _ := <span class="pkg">strconv</span>.<span class="fn">ParseFloat</span>(<span class="str">"3.14"</span>, <span class="num">32</span>)
f32 := <span class="typ">float32</span>(v)</pre>
</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">FormatFloat</span>
<span class="card-badge badge-gold">FormatFloat</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// FormatFloat(f, fmt, prec, bitSize)</span>
<span class="cmt">// fmt: 'f' decimal, 'e' scientific, 'g' shortest, 'x' hex</span>
<span class="cmt">// prec: decimal places (-1 = shortest representation)</span>
f := <span class="num">3.14159</span>
<span class="pkg">strconv</span>.<span class="fn">FormatFloat</span>(f, <span class="str">'f'</span>, <span class="num">2</span>, <span class="num">64</span>) <span class="cmt">// "3.14"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatFloat</span>(f, <span class="str">'f'</span>, <span class="num">4</span>, <span class="num">64</span>) <span class="cmt">// "3.1416"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatFloat</span>(f, <span class="str">'e'</span>, <span class="num">3</span>, <span class="num">64</span>) <span class="cmt">// "3.142e+00"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatFloat</span>(f, <span class="str">'g'</span>, -<span class="num">1</span>, <span class="num">64</span>) <span class="cmt">// "3.14159" (shortest)</span>
<span class="pkg">strconv</span>.<span class="fn">FormatFloat</span>(f, <span class="str">'g'</span>, <span class="num">3</span>, <span class="num">64</span>) <span class="cmt">// "3.14"</span></pre>
</div>
</div>
</div>
</section>
<!-- ── 4. PARSEBOOL / FORMATBOOL ─────────────────────── -->
<section class="section" id="bools">
<div class="section-header">
<div class="section-icon icon-purple">✅</div>
<h2>Booleans — Parse & Format</h2>
<span class="section-tag">ParseBool · FormatBool</span>
</div>
<div class="two-col">
<div class="card">
<div class="card-header">
<span class="card-title">ParseBool — flexible boolean parsing</span>
<span class="card-badge badge-purple">ParseBool</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// Accepts many truthy/falsy string forms</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"true"</span>) <span class="cmt">// true, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"TRUE"</span>) <span class="cmt">// true, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"1"</span>) <span class="cmt">// true, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"t"</span>) <span class="cmt">// true, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"T"</span>) <span class="cmt">// true, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"false"</span>) <span class="cmt">// false, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"FALSE"</span>) <span class="cmt">// false, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"0"</span>) <span class="cmt">// false, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"f"</span>) <span class="cmt">// false, nil</span>
<span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="str">"yes"</span>) <span class="cmt">// false, ErrSyntax</span></pre>
</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">FormatBool & usage pattern</span>
<span class="card-badge badge-purple">FormatBool</span>
</div>
<div class="code-wrap">
<pre><span class="pkg">strconv</span>.<span class="fn">FormatBool</span>(<span class="kw">true</span>) <span class="cmt">// "true"</span>
<span class="pkg">strconv</span>.<span class="fn">FormatBool</span>(<span class="kw">false</span>) <span class="cmt">// "false"</span>
<span class="cmt">// Common pattern: parse feature flags from env</span>
<span class="fn">isEnabled</span> := <span class="kw">func</span>(key <span class="typ">string</span>) <span class="typ">bool</span> {
v, err := <span class="pkg">strconv</span>.<span class="fn">ParseBool</span>(<span class="pkg">os</span>.<span class="fn">Getenv</span>(key))
<span class="kw">return</span> err == <span class="kw">nil</span> && v
}
<span class="kw">if</span> <span class="fn">isEnabled</span>(<span class="str">"FEATURE_DARK_MODE"</span>) {
<span class="cmt">// enable dark mode</span>
}</pre>
</div>
</div>
</div>
</section>
<!-- ── 5. QUOTE / UNQUOTE ────────────────────────────── -->
<section class="section" id="quote">
<div class="section-header">
<div class="section-icon icon-red">💬</div>
<h2>Quote & Unquote</h2>
<span class="section-tag">Quote · QuoteRune · Unquote</span>
</div>
<div class="callout">
<span class="callout-icon">ℹ️</span>
<div><code>Quote</code> produces a Go string literal with escape sequences for special characters — useful for logging, debugging, or generating Go source. <code>Unquote</code> reverses it.</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">Quote — wrap in double quotes with escaping</span>
<span class="card-badge badge-red">Quote</span>
</div>
<div class="code-wrap">
<pre><span class="pkg">strconv</span>.<span class="fn">Quote</span>(<span class="str">"Hello, World"</span>) <span class="cmt">// `"Hello, World"`</span>
<span class="pkg">strconv</span>.<span class="fn">Quote</span>(<span class="str">"tab\there"</span>) <span class="cmt">// `"tab\there"`</span>
<span class="pkg">strconv</span>.<span class="fn">Quote</span>(<span class="str">"new\nline"</span>) <span class="cmt">// `"new\nline"`</span>
<span class="pkg">strconv</span>.<span class="fn">Quote</span>(<span class="str">`say "hi"`</span>) <span class="cmt">// `"say \"hi\""`</span>
<span class="pkg">strconv</span>.<span class="fn">Quote</span>(<span class="str">"日本語"</span>) <span class="cmt">// `"日本語"` (printable Unicode kept)</span>
<span class="cmt">// QuoteToASCII — escapes non-ASCII as \uXXXX</span>
<span class="pkg">strconv</span>.<span class="fn">QuoteToASCII</span>(<span class="str">"日本語"</span>) <span class="cmt">// `"日本語"`</span>
<span class="cmt">// QuoteRune — quote a single rune</span>
<span class="pkg">strconv</span>.<span class="fn">QuoteRune</span>(<span class="str">'A'</span>) <span class="cmt">// `'A'`</span>
<span class="pkg">strconv</span>.<span class="fn">QuoteRune</span>(<span class="str">'\n'</span>) <span class="cmt">// `'\n'`</span>
<span class="pkg">strconv</span>.<span class="fn">QuoteRune</span>(<span class="str">'日'</span>) <span class="cmt">// `'日'`</span></pre>
</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">Unquote — parse a quoted string literal</span>
<span class="card-badge badge-red">Unquote</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// Unquote interprets a Go string literal</span>
s, err := <span class="pkg">strconv</span>.<span class="fn">Unquote</span>(<span class="str">`"Hello\nWorld"`)
<span class="cmt">// s = "Hello\nWorld" (actual newline), err = nil</span>
s, err = <span class="pkg">strconv</span>.<span class="fn">Unquote</span>(<span class="str">`"tab\there"`)
<span class="cmt">// s = "tab\there" (actual tab), err = nil</span>
s, err = <span class="pkg">strconv</span>.<span class="fn">Unquote</span>(<span class="str">`"say \"hi\""`)
<span class="cmt">// s = `say "hi"`, err = nil</span>
<span class="cmt">// Backtick (raw) strings also work</span>
s, err = <span class="pkg">strconv</span>.<span class="fn">Unquote</span>(<span class="str">"`raw\nstring`"</span>)
<span class="cmt">// s = "raw\\nstring" (backslash not interpreted)</span></pre>
</div>
</div>
</section>
<!-- ── 6. ERROR HANDLING ──────────────────────────────── -->
<section class="section" id="errors">
<div class="section-header">
<div class="section-icon icon-gold">⚠️</div>
<h2>Error Handling</h2>
<span class="section-tag">NumError · ErrRange · ErrSyntax</span>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">NumError — inspect parse failures</span>
<span class="card-badge badge-gold">NumError</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// Parse functions return *strconv.NumError on failure</span>
_, err := <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(<span class="str">"abc"</span>)
<span class="kw">if</span> err != <span class="kw">nil</span> {
<span class="kw">var</span> ne *<span class="pkg">strconv</span>.<span class="typ">NumError</span>
<span class="kw">if</span> <span class="pkg">errors</span>.<span class="fn">As</span>(err, &ne) {
ne.Func <span class="cmt">// "Atoi"</span>
ne.Num <span class="cmt">// "abc" (the input)</span>
ne.Err <span class="cmt">// strconv.ErrSyntax or strconv.ErrRange</span>
}
}
<span class="cmt">// Two sentinel errors to check for</span>
<span class="pkg">errors</span>.<span class="fn">Is</span>(err, <span class="pkg">strconv</span>.ErrSyntax) <span class="cmt">// invalid characters</span>
<span class="pkg">errors</span>.<span class="fn">Is</span>(err, <span class="pkg">strconv</span>.ErrRange) <span class="cmt">// value out of range for type</span>
<span class="cmt">// ErrRange example</span>
_, err = <span class="pkg">strconv</span>.<span class="fn">ParseInt</span>(<span class="str">"999"</span>, <span class="num">10</span>, <span class="num">8</span>) <span class="cmt">// overflows int8 (max 127)</span>
<span class="pkg">errors</span>.<span class="fn">Is</span>(err, <span class="pkg">strconv</span>.ErrRange) <span class="cmt">// true</span></pre>
</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">Patterns for parsing user input</span>
<span class="card-badge badge-blue">Patterns</span>
</div>
<div class="code-wrap">
<pre><span class="cmt">// Parse with default fallback</span>
<span class="fn">parseInt</span> := <span class="kw">func</span>(s <span class="typ">string</span>, def <span class="typ">int</span>) <span class="typ">int</span> {
n, err := <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(s)
<span class="kw">if</span> err != <span class="kw">nil</span> {
<span class="kw">return</span> def
}
<span class="kw">return</span> n
}
port := <span class="fn">parseInt</span>(<span class="pkg">os</span>.<span class="fn">Getenv</span>(<span class="str">"PORT"</span>), <span class="num">8080</span>)
<span class="cmt">// Parse with range validation</span>
raw := <span class="pkg">os</span>.<span class="fn">Getenv</span>(<span class="str">"WORKERS"</span>)
workers, err := <span class="pkg">strconv</span>.<span class="fn">Atoi</span>(raw)
<span class="kw">if</span> err != <span class="kw">nil</span> || workers < <span class="num">1</span> || workers > <span class="num">100</span> {
<span class="kw">return</span> <span class="pkg">fmt</span>.<span class="fn">Errorf</span>(<span class="str">"WORKERS must be 1-100, got %q"</span>, raw)
}</pre>
</div>
</div>
</section>
<!-- ── 7. APPEND VARIANTS ────────────────────────────── -->
<section class="section" id="append">
<div class="section-header">
<div class="section-icon icon-green">➕</div>
<h2>Append Variants</h2>
<span class="section-tag">AppendInt · AppendFloat · AppendBool</span>
</div>
<div class="callout tip">
<span class="callout-icon">💡</span>
<div>The <code>Append*</code> variants write directly into a <code>[]byte</code> without allocating a new string. Use them in tight loops or when building byte slices incrementally.</div>
</div>
<div class="card">
<div class="card-header">
<span class="card-title">AppendInt, AppendFloat, AppendBool — zero-alloc formatting</span>
<span class="card-badge badge-green">Append*</span>
</div>
<div class="code-wrap">
<pre>buf := []<span class="typ">byte</span>(<span class="str">"value="</span>)
buf = <span class="pkg">strconv</span>.<span class="fn">AppendInt</span>(buf, <span class="num">42</span>, <span class="num">10</span>)
<span class="cmt">// buf = "value=42"</span>
buf = <span class="fn">append</span>(buf, <span class="str">' '</span>)
buf = <span class="pkg">strconv</span>.<span class="fn">AppendFloat</span>(buf, <span class="num">3.14</span>, <span class="str">'f'</span>, <span class="num">2</span>, <span class="num">64</span>)
<span class="cmt">// buf = "value=42 3.14"</span>
buf = <span class="fn">append</span>(buf, <span class="str">' '</span>)
buf = <span class="pkg">strconv</span>.<span class="fn">AppendBool</span>(buf, <span class="kw">true</span>)
<span class="cmt">// buf = "value=42 3.14 true"</span>
buf = <span class="pkg">strconv</span>.<span class="fn">AppendQuote</span>(buf[:0], <span class="str">"hello\nworld"</span>)
<span class="cmt">// buf = `"hello\nworld"`</span>
<span class="pkg">fmt</span>.<span class="fn">Println</span>(<span class="typ">string</span>(buf))</pre>
</div>
</div>
</section>
<!-- ── REFERENCE TABLE ───────────────────────────────── -->
<section class="section" id="reference">
<div class="section-header">
<div class="section-icon icon-blue">📋</div>
<h2>Quick Reference</h2>
<span class="section-tag">All key functions</span>
</div>
<table class="ref-table">
<thead>
<tr><th>Function</th><th>Returns</th><th>Description</th></tr>
</thead>
<tbody>
<tr><td>strconv.Atoi(s)</td><td>int, error</td><td>Parse base-10 string to int</td></tr>
<tr><td>strconv.Itoa(i)</td><td>string</td><td>Format int to base-10 string</td></tr>
<tr><td>strconv.ParseInt(s, base, bitSize)</td><td>int64, error</td><td>Parse signed integer in any base (2–36); bitSize limits range</td></tr>
<tr><td>strconv.ParseUint(s, base, bitSize)</td><td>uint64, error</td><td>Parse unsigned integer in any base</td></tr>
<tr><td>strconv.FormatInt(i, base)</td><td>string</td><td>Format int64 in any base</td></tr>
<tr><td>strconv.FormatUint(u, base)</td><td>string</td><td>Format uint64 in any base</td></tr>
<tr><td>strconv.ParseFloat(s, bitSize)</td><td>float64, error</td><td>Parse decimal or scientific notation float</td></tr>
<tr><td>strconv.FormatFloat(f, fmt, prec, bitSize)</td><td>string</td><td>Format float; fmt='f'/'e'/'g'/'x', prec=-1 for shortest</td></tr>
<tr><td>strconv.ParseBool(s)</td><td>bool, error</td><td>Parse "1","t","true","T","TRUE","false","0","f","F","FALSE"</td></tr>
<tr><td>strconv.FormatBool(b)</td><td>string</td><td>"true" or "false"</td></tr>
<tr><td>strconv.Quote(s)</td><td>string</td><td>Wrap in double quotes, escape special chars</td></tr>
<tr><td>strconv.QuoteToASCII(s)</td><td>string</td><td>Like Quote but escapes non-ASCII as \uXXXX</td></tr>
<tr><td>strconv.QuoteRune(r)</td><td>string</td><td>Single-quote a rune with escaping</td></tr>
<tr><td>strconv.Unquote(s)</td><td>string, error</td><td>Parse a Go string or char literal</td></tr>
<tr><td>strconv.AppendInt(dst, i, base)</td><td>[]byte</td><td>Append formatted int to byte slice</td></tr>
<tr><td>strconv.AppendFloat(dst, f, fmt, prec, bitSize)</td><td>[]byte</td><td>Append formatted float to byte slice</td></tr>
<tr><td>strconv.AppendBool(dst, b)</td><td>[]byte</td><td>Append "true" or "false" to byte slice</td></tr>
<tr><td>strconv.AppendQuote(dst, s)</td><td>[]byte</td><td>Append quoted string to byte slice</td></tr>
<tr><td>strconv.ErrSyntax</td><td>error</td><td>Sentinel: input is not valid for the type</td></tr>
<tr><td>strconv.ErrRange</td><td>error</td><td>Sentinel: value overflows the target type</td></tr>
</tbody>
</table>
</section>
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<li><a href="#atoi-itoa">1 — Atoi & Itoa</a></li>
<li><a href="#integers">2 — Integers</a></li>
<li><a href="#floats">3 — Floats</a></li>
<li><a href="#bools">4 — Booleans</a></li>
<li><a href="#quote">5 — Quote & Unquote</a></li>
<li><a href="#errors">6 — Error Handling</a></li>
<li><a href="#append">7 — Append Variants</a></li>
<li><a href="#reference">99 — Quick Reference</a></li>
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