summaryrefslogtreecommitdiff
path: root/docs/CODE_STYLE.md
blob: e27778e32e7118f648147e81b8a5c314ffe26255 (plain)
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
# curl C code style

Source code that has a common style is easier to read than code that uses
different styles in different places. It helps making the code feel like one
single code base. Easy-to-read is a very important property of code and helps
making it easier to review when new things are added and it helps debugging
code when developers are trying to figure out why things go wrong. A unified
style is more important than individual contributors having their own personal
tastes satisfied.

Our C code has a few style rules. Most of them are verified and upheld by the
`lib/checksrc.pl` script. Invoked with `make checksrc` or even by default by
the build system when built after `./configure --enable-debug` has been used.

It is normally not a problem for anyone to follow the guidelines, as you just
need to copy the style already used in the source code and there are no
particularly unusual rules in our set of rules.

We also work hard on writing code that are warning-free on all the major
platforms and in general on as many platforms as possible. Code that obviously
will cause warnings will not be accepted as-is.

## Naming

Try using a non-confusing naming scheme for your new functions and variable
names. It doesn't necessarily have to mean that you should use the same as in
other places of the code, just that the names should be logical,
understandable and be named according to what they're used for. File-local
functions should be made static. We like lower case names.

See the [INTERNALS](https://curl.se/dev/internals.html#symbols) document on
how we name non-exported library-global symbols.

## Indenting

We use only spaces for indentation, never TABs. We use two spaces for each new
open brace.

```c
if(something_is_true) {
  while(second_statement == fine) {
    moo();
  }
}
```

## Comments

Since we write C89 code, **//** comments are not allowed. They weren't
introduced in the C standard until C99. We use only **/* comments */**.

```c
/* this is a comment */
```

## Long lines

Source code in curl may never be wider than 79 columns and there are two
reasons for maintaining this even in the modern era of very large and high
resolution screens:

1. Narrower columns are easier to read than very wide ones. There's a reason
   newspapers have used columns for decades or centuries.

2. Narrower columns allow developers to easier show multiple pieces of code
   next to each other in different windows. I often have two or three source
   code windows next to each other on the same screen - as well as multiple
   terminal and debugging windows.

## Braces

In if/while/do/for expressions, we write the open brace on the same line as
the keyword and we then set the closing brace on the same indentation level as
the initial keyword. Like this:

```c
if(age < 40) {
  /* clearly a youngster */
}
```

You may omit the braces if they would contain only a one-line statement:

```c
if(!x)
  continue;
```

For functions the opening brace should be on a separate line:

```c
int main(int argc, char **argv)
{
  return 1;
}
```

## 'else' on the following line

When adding an **else** clause to a conditional expression using braces, we
add it on a new line after the closing brace. Like this:

```c
if(age < 40) {
  /* clearly a youngster */
}
else {
  /* probably grumpy */
}
```

## No space before parentheses

When writing expressions using if/while/do/for, there shall be no space
between the keyword and the open parenthesis. Like this:

```c
while(1) {
  /* loop forever */
}
```

## Use boolean conditions

Rather than test a conditional value such as a bool against TRUE or FALSE, a
pointer against NULL or != NULL and an int against zero or not zero in
if/while conditions we prefer:

```c
result = do_something();
if(!result) {
  /* something went wrong */
  return result;
}
```

## No assignments in conditions

To increase readability and reduce complexity of conditionals, we avoid
assigning variables within if/while conditions. We frown upon this style:

```c
if((ptr = malloc(100)) == NULL)
  return NULL;
```

and instead we encourage the above version to be spelled out more clearly:

```c
ptr = malloc(100);
if(!ptr)
  return NULL;
```

## New block on a new line

We never write multiple statements on the same source line, even for very
short if() conditions.

```c
if(a)
  return TRUE;
else if(b)
  return FALSE;
```

and NEVER:

```c
if(a) return TRUE;
else if(b) return FALSE;
```

## Space around operators

Please use spaces on both sides of operators in C expressions.  Postfix **(),
[], ->, ., ++, --** and Unary **+, - !, ~, &** operators excluded they should
have no space.

Examples:

```c
bla = func();
who = name[0];
age += 1;
true = !false;
size += -2 + 3 * (a + b);
ptr->member = a++;
struct.field = b--;
ptr = &address;
contents = *pointer;
complement = ~bits;
empty = (!*string) ? TRUE : FALSE;
```

## No parentheses for return values

We use the 'return' statement without extra parentheses around the value:

```c
int works(void)
{
  return TRUE;
}
```

## Parentheses for sizeof arguments

When using the sizeof operator in code, we prefer it to be written with
parentheses around its argument:

```c
int size = sizeof(int);
```

## Column alignment

Some statements cannot be completed on a single line because the line would be
too long, the statement too hard to read, or due to other style guidelines
above. In such a case the statement will span multiple lines.

If a continuation line is part of an expression or sub-expression then you
should align on the appropriate column so that it's easy to tell what part of
the statement it is. Operators should not start continuation lines. In other
cases follow the 2-space indent guideline. Here are some examples from
libcurl:

```c
if(Curl_pipeline_wanted(handle->multi, CURLPIPE_HTTP1) &&
   (handle->set.httpversion != CURL_HTTP_VERSION_1_0) &&
   (handle->set.httpreq == HTTPREQ_GET ||
    handle->set.httpreq == HTTPREQ_HEAD))
  /* didn't ask for HTTP/1.0 and a GET or HEAD */
  return TRUE;
```

If no parenthesis, use the default indent:

```c
data->set.http_disable_hostname_check_before_authentication =
  (0 != va_arg(param, long)) ? TRUE : FALSE;
```

Function invoke with an open parenthesis:

```c
if(option) {
  result = parse_login_details(option, strlen(option),
                               (userp ? &user : NULL),
                               (passwdp ? &passwd : NULL),
                               NULL);
}
```

Align with the "current open" parenthesis:

```c
DEBUGF(infof(data, "Curl_pp_readresp_ %d bytes of trailing "
             "server response left\n",
             (int)clipamount));
```

## Platform dependent code

Use **#ifdef HAVE_FEATURE** to do conditional code. We avoid checking for
particular operating systems or hardware in the #ifdef lines. The HAVE_FEATURE
shall be generated by the configure script for unix-like systems and they are
hard-coded in the `config-[system].h` files for the others.

We also encourage use of macros/functions that possibly are empty or defined
to constants when libcurl is built without that feature, to make the code
seamless. Like this example where the **magic()** function works differently
depending on a build-time conditional:

```c
#ifdef HAVE_MAGIC
void magic(int a)
{
  return a + 2;
}
#else
#define magic(x) 1
#endif

int content = magic(3);
```

## No typedefed structs

Use structs by all means, but do not typedef them. Use the `struct name` way
of identifying them:

```c
struct something {
   void *valid;
   size_t way_to_write;
};
struct something instance;
```

**Not okay**:

```c
typedef struct {
   void *wrong;
   size_t way_to_write;
} something;
something instance;
```