forked from mmcgrana/gobyexample
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathstring-formatting
460 lines (363 loc) · 18.8 KB
/
string-formatting
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: String Formatting</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'string-functions';
}
if (e.key == "ArrowRight") {
window.location.href = 'text-templates';
}
}
</script>
<body>
<div class="example" id="string-formatting">
<h2><a href="./">Go by Example</a>: String Formatting</h2>
<table>
<tr>
<td class="docs">
<p>Go offers excellent support for string formatting in
the <code>printf</code> tradition. Here are some examples of
common string formatting tasks.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/EZCZX1Uwp6D"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"os"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">type</span> <span class="nx">point</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">x</span><span class="p">,</span> <span class="nx">y</span> <span class="kt">int</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Go offers several printing “verbs” designed to
format general Go values. For example, this prints
an instance of our <code>point</code> struct.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">p</span> <span class="o">:=</span> <span class="nx">point</span><span class="p">{</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"struct1: %v\n"</span><span class="p">,</span> <span class="nx">p</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>If the value is a struct, the <code>%+v</code> variant will
include the struct’s field names.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"struct2: %+v\n"</span><span class="p">,</span> <span class="nx">p</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>The <code>%#v</code> variant prints a Go syntax representation
of the value, i.e. the source code snippet that
would produce that value.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"struct3: %#v\n"</span><span class="p">,</span> <span class="nx">p</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>To print the type of a value, use <code>%T</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"type: %T\n"</span><span class="p">,</span> <span class="nx">p</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Formatting booleans is straight-forward.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"bool: %t\n"</span><span class="p">,</span> <span class="kc">true</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>There are many options for formatting integers.
Use <code>%d</code> for standard, base-10 formatting.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"int: %d\n"</span><span class="p">,</span> <span class="mi">123</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This prints a binary representation.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"bin: %b\n"</span><span class="p">,</span> <span class="mi">14</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This prints the character corresponding to the
given integer.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"char: %c\n"</span><span class="p">,</span> <span class="mi">33</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>%x</code> provides hex encoding.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"hex: %x\n"</span><span class="p">,</span> <span class="mi">456</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>There are also several formatting options for
floats. For basic decimal formatting use <code>%f</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"float1: %f\n"</span><span class="p">,</span> <span class="mf">78.9</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>%e</code> and <code>%E</code> format the float in (slightly
different versions of) scientific notation.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"float2: %e\n"</span><span class="p">,</span> <span class="mf">123400000.0</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"float3: %E\n"</span><span class="p">,</span> <span class="mf">123400000.0</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>For basic string printing use <code>%s</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"str1: %s\n"</span><span class="p">,</span> <span class="s">"\"string\""</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>To double-quote strings as in Go source, use <code>%q</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"str2: %q\n"</span><span class="p">,</span> <span class="s">"\"string\""</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>As with integers seen earlier, <code>%x</code> renders
the string in base-16, with two output characters
per byte of input.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"str3: %x\n"</span><span class="p">,</span> <span class="s">"hex this"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>To print a representation of a pointer, use <code>%p</code>.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"pointer: %p\n"</span><span class="p">,</span> <span class="o">&</span><span class="nx">p</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>When formatting numbers you will often want to
control the width and precision of the resulting
figure. To specify the width of an integer, use a
number after the <code>%</code> in the verb. By default the
result will be right-justified and padded with
spaces.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"width1: |%6d|%6d|\n"</span><span class="p">,</span> <span class="mi">12</span><span class="p">,</span> <span class="mi">345</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>You can also specify the width of printed floats,
though usually you’ll also want to restrict the
decimal precision at the same time with the
width.precision syntax.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"width2: |%6.2f|%6.2f|\n"</span><span class="p">,</span> <span class="mf">1.2</span><span class="p">,</span> <span class="mf">3.45</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>To left-justify, use the <code>-</code> flag.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"width3: |%-6.2f|%-6.2f|\n"</span><span class="p">,</span> <span class="mf">1.2</span><span class="p">,</span> <span class="mf">3.45</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>You may also want to control width when formatting
strings, especially to ensure that they align in
table-like output. For basic right-justified width.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"width4: |%6s|%6s|\n"</span><span class="p">,</span> <span class="s">"foo"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>To left-justify use the <code>-</code> flag as with numbers.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">"width5: |%-6s|%-6s|\n"</span><span class="p">,</span> <span class="s">"foo"</span><span class="p">,</span> <span class="s">"b"</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>So far we’ve seen <code>Printf</code>, which prints the
formatted string to <code>os.Stdout</code>. <code>Sprintf</code> formats
and returns a string without printing it anywhere.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">s</span> <span class="o">:=</span> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Sprintf</span><span class="p">(</span><span class="s">"sprintf: a %s"</span><span class="p">,</span> <span class="s">"string"</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">s</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>You can format+print to <code>io.Writers</code> other than
<code>os.Stdout</code> using <code>Fprintf</code>.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Fprintf</span><span class="p">(</span><span class="nx">os</span><span class="p">.</span><span class="nx">Stderr</span><span class="p">,</span> <span class="s">"io: an %s\n"</span><span class="p">,</span> <span class="s">"error"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run string-formatting.go
<span class="go">struct1: {1 2}
</span><span class="go">struct2: {x:1 y:2}
</span><span class="go">struct3: main.point{x:1, y:2}
</span><span class="go">type: main.point
</span><span class="go">bool: true
</span><span class="go">int: 123
</span><span class="go">bin: 1110
</span><span class="go">char: !
</span><span class="go">hex: 1c8
</span><span class="go">float1: 78.900000
</span><span class="go">float2: 1.234000e+08
</span><span class="go">float3: 1.234000E+08
</span><span class="go">str1: "string"
</span><span class="go">str2: "\"string\""
</span><span class="go">str3: 6865782074686973
</span><span class="go">pointer: 0xc0000ba000
</span><span class="go">width1: | 12| 345|
</span><span class="go">width2: | 1.20| 3.45|
</span><span class="go">width3: |1.20 |3.45 |
</span><span class="go">width4: | foo| b|
</span><span class="go">width5: |foo |b |
</span><span class="go">sprintf: a string
</span><span class="go">io: an error</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="text-templates">Text Templates</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
<script>
var codeLines = [];
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"os\"\u000A)\u000A');codeLines.push('type point struct {\u000A x, y int\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' p :\u003D point{1, 2}\u000A fmt.Printf(\"struct1: %v\\n\", p)\u000A');codeLines.push(' fmt.Printf(\"struct2: %+v\\n\", p)\u000A');codeLines.push(' fmt.Printf(\"struct3: %#v\\n\", p)\u000A');codeLines.push(' fmt.Printf(\"type: %T\\n\", p)\u000A');codeLines.push(' fmt.Printf(\"bool: %t\\n\", true)\u000A');codeLines.push(' fmt.Printf(\"int: %d\\n\", 123)\u000A');codeLines.push(' fmt.Printf(\"bin: %b\\n\", 14)\u000A');codeLines.push(' fmt.Printf(\"char: %c\\n\", 33)\u000A');codeLines.push(' fmt.Printf(\"hex: %x\\n\", 456)\u000A');codeLines.push(' fmt.Printf(\"float1: %f\\n\", 78.9)\u000A');codeLines.push(' fmt.Printf(\"float2: %e\\n\", 123400000.0)\u000A fmt.Printf(\"float3: %E\\n\", 123400000.0)\u000A');codeLines.push(' fmt.Printf(\"str1: %s\\n\", \"\\\"string\\\"\")\u000A');codeLines.push(' fmt.Printf(\"str2: %q\\n\", \"\\\"string\\\"\")\u000A');codeLines.push(' fmt.Printf(\"str3: %x\\n\", \"hex this\")\u000A');codeLines.push(' fmt.Printf(\"pointer: %p\\n\", \u0026p)\u000A');codeLines.push(' fmt.Printf(\"width1: |%6d|%6d|\\n\", 12, 345)\u000A');codeLines.push(' fmt.Printf(\"width2: |%6.2f|%6.2f|\\n\", 1.2, 3.45)\u000A');codeLines.push(' fmt.Printf(\"width3: |%-6.2f|%-6.2f|\\n\", 1.2, 3.45)\u000A');codeLines.push(' fmt.Printf(\"width4: |%6s|%6s|\\n\", \"foo\", \"b\")\u000A');codeLines.push(' fmt.Printf(\"width5: |%-6s|%-6s|\\n\", \"foo\", \"b\")\u000A');codeLines.push(' s :\u003D fmt.Sprintf(\"sprintf: a %s\", \"string\")\u000A fmt.Println(s)\u000A');codeLines.push(' fmt.Fprintf(os.Stderr, \"io: an %s\\n\", \"error\")\u000A}\u000A');codeLines.push('');
</script>
<script src="site.js" async></script>
</body>
</html>