tmp/tmpq_hxyo5v/{from.md → to.md}
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| 1 |
+
### General <a id="cpp.embed.gen">[[cpp.embed.gen]]</a>
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| 2 |
+
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| 3 |
+
A *bracket resource search* for a sequence of characters searches a
|
| 4 |
+
sequence of places for a resource identified uniquely by that sequence
|
| 5 |
+
of characters. How the places are determined or the resource identified
|
| 6 |
+
is *implementation-defined*.
|
| 7 |
+
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| 8 |
+
A *quote resource search* for a sequence of characters attempts to
|
| 9 |
+
identify a resource that is named by the sequence of characters. The
|
| 10 |
+
named resource is searched for in an *implementation-defined* manner. If
|
| 11 |
+
the implementation does not support a quote resource search for that
|
| 12 |
+
sequence of characters, or if the search fails, the result of the quote
|
| 13 |
+
resource search is the result of a bracket resource search for the same
|
| 14 |
+
sequence of characters.
|
| 15 |
+
|
| 16 |
+
A preprocessing directive of the form
|
| 17 |
+
|
| 18 |
+
``` bnf
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| 19 |
+
'# embed' header-name pp-tokensₒₚₜ new-line
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| 20 |
+
```
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| 21 |
+
|
| 22 |
+
causes the replacement of that directive by preprocessing tokens derived
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| 23 |
+
from data in the resource identified by *header-name*, as specified
|
| 24 |
+
below.
|
| 25 |
+
|
| 26 |
+
If the *header-name* is of the form
|
| 27 |
+
|
| 28 |
+
``` bnf
|
| 29 |
+
'<' h-char-sequence '>'
|
| 30 |
+
```
|
| 31 |
+
|
| 32 |
+
the resource is identified by a bracket resource search for the sequence
|
| 33 |
+
of characters of the *h-char-sequence*.
|
| 34 |
+
|
| 35 |
+
If the *header-name* is of the form
|
| 36 |
+
|
| 37 |
+
``` bnf
|
| 38 |
+
'"' q-char-sequence '"'
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| 39 |
+
```
|
| 40 |
+
|
| 41 |
+
the resource is identified by a quote resource search for the sequence
|
| 42 |
+
of characters of the *q-char-sequence*.
|
| 43 |
+
|
| 44 |
+
If a bracket resource search fails, or if a quote or bracket resource
|
| 45 |
+
search identifies a resource that cannot be processed by the
|
| 46 |
+
implementation, the program is ill-formed.
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| 47 |
+
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| 48 |
+
[*Note 1*: If the resource cannot be processed, the program is
|
| 49 |
+
ill-formed even when processing `#embed` with `limit(0)`
|
| 50 |
+
[[cpp.embed.param.limit]] or evaluating `__has_embed`. — *end note*]
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| 51 |
+
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| 52 |
+
*Recommended practice:* A mechanism similar to, but distinct from, the
|
| 53 |
+
*implementation-defined* search paths used for `#include`
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| 54 |
+
[[cpp.include]] is encouraged.
|
| 55 |
+
|
| 56 |
+
Either form of the `#embed` directive processes the *pp-tokens*, if
|
| 57 |
+
present, just as in normal text. The *pp-tokens* shall then have the
|
| 58 |
+
form *embed-parameter-seq*.
|
| 59 |
+
|
| 60 |
+
A resource is a source of data accessible from the translation
|
| 61 |
+
environment. A resource has an *implementation-resource-width*, which is
|
| 62 |
+
the *implementation-defined* size in bits of the resource. If the
|
| 63 |
+
implementation-resource-width is not an integral multiple of `CHAR_BIT`,
|
| 64 |
+
the program is ill-formed. Let *implementation-resource-count* be
|
| 65 |
+
implementation-resource-width divided by `CHAR_BIT`. Every resource also
|
| 66 |
+
has a *resource-count*, which is
|
| 67 |
+
|
| 68 |
+
- the value as computed from the optionally-provided `limit`
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| 69 |
+
*embed-parameter* [[cpp.embed.param.limit]], if present;
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| 70 |
+
- otherwise, the implementation-resource-count.
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| 71 |
+
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| 72 |
+
A resource is empty if the resource-count is zero.
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| 73 |
+
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| 74 |
+
[*Example 1*:
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| 75 |
+
|
| 76 |
+
``` cpp
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| 77 |
+
// ill-formed if the implementation-resource-width is 6 bits
|
| 78 |
+
#embed "6_bits.bin"
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| 79 |
+
```
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| 80 |
+
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| 81 |
+
— *end example*]
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| 82 |
+
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| 83 |
+
The `#embed` directive is replaced by a comma-separated list of integer
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| 84 |
+
literals of type `int`, unless otherwise modified by embed parameters
|
| 85 |
+
[[cpp.embed.param]].
|
| 86 |
+
|
| 87 |
+
The integer literals in the comma-separated list correspond to
|
| 88 |
+
resource-count consecutive calls to `std::fgetc` [[cstdio.syn]] from the
|
| 89 |
+
resource, as a binary file. If any call to `std::fgetc` returns `EOF`,
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| 90 |
+
the program is ill-formed.
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| 91 |
+
|
| 92 |
+
*Recommended practice:* The value of each integer literal should closely
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| 93 |
+
represent the bit stream of the resource unmodified. This can require an
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| 94 |
+
implementation to consider potential differences between translation and
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| 95 |
+
execution environments, as well as any other applicable sources of
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| 96 |
+
mismatch.
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| 97 |
+
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| 98 |
+
[*Example 2*:
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| 99 |
+
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| 100 |
+
``` cpp
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| 101 |
+
#include <cstring>
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| 102 |
+
#include <cstddef>
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| 103 |
+
#include <fstream>
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| 104 |
+
#include <vector>
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| 105 |
+
#include <cassert>
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| 106 |
+
|
| 107 |
+
int main() {
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| 108 |
+
// If the file is the same as the resource in the translation environment, no assert in this program should fail.
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| 109 |
+
constexpr unsigned char d[] = {
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| 110 |
+
#embed <data.dat>
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| 111 |
+
};
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| 112 |
+
const std::vector<unsigned char> vec_d = {
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| 113 |
+
#embed <data.dat>
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| 114 |
+
};
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| 115 |
+
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| 116 |
+
constexpr std::size_t expected_size = sizeof(d);
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| 117 |
+
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| 118 |
+
// same file in execution environment as was embedded
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| 119 |
+
std::ifstream f_source("data.dat", std::ios::binary | std::ios::in);
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| 120 |
+
unsigned char runtime_d[expected_size];
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| 121 |
+
char* ifstream_ptr = reinterpret_cast<char*>(runtime_d);
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| 122 |
+
assert(!f_source.read(ifstream_ptr, expected_size));
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| 123 |
+
std::size_t ifstream_size = f_source.gcount();
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| 124 |
+
assert (ifstream_size == expected_size);
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| 125 |
+
int is_same = std::memcmp(&d[0], ifstream_ptr, ifstream_size);
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| 126 |
+
assert(is_same == 0);
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| 127 |
+
int is_same_vec = std::memcmp(vec_d.data(), ifstream_ptr, ifstream_size);
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| 128 |
+
assert(is_same_vec == 0);
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| 129 |
+
}
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| 130 |
+
```
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| 131 |
+
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| 132 |
+
— *end example*]
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| 133 |
+
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| 134 |
+
[*Example 3*:
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| 135 |
+
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| 136 |
+
``` cpp
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| 137 |
+
int i = {
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| 138 |
+
#embed "i.dat"
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| 139 |
+
}; // well-formed if i.dat produces a single value
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| 140 |
+
int i2 =
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| 141 |
+
#embed "i.dat"
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| 142 |
+
; // also well-formed if i.dat produces a single value
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| 143 |
+
struct s {
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| 144 |
+
double a, b, c;
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| 145 |
+
struct { double e, f, g; } x;
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| 146 |
+
double h, i, j;
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| 147 |
+
};
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| 148 |
+
s x = {
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| 149 |
+
// well-formed if the directive produces nine or fewer values
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| 150 |
+
#embed "s.dat"
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| 151 |
+
};
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| 152 |
+
```
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| 153 |
+
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| 154 |
+
— *end example*]
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| 155 |
+
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| 156 |
+
A preprocessing directive of the form
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| 157 |
+
|
| 158 |
+
``` bnf
|
| 159 |
+
'# embed' pp-tokens new-line
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| 160 |
+
```
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| 161 |
+
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| 162 |
+
(that does not match the previous form) is permitted. The preprocessing
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| 163 |
+
tokens after `embed` in the directive are processed just as in normal
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| 164 |
+
text (i.e., each identifier currently defined as a macro name is
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| 165 |
+
replaced by its replacement list of preprocessing tokens). Then, an
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| 166 |
+
attempt is made to form a *header-name* preprocessing token
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| 167 |
+
[[lex.header]] from the whitespace and the characters of the spellings
|
| 168 |
+
of the resulting sequence of preprocessing tokens immediately after
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| 169 |
+
`embed`; the treatment of whitespace is *implementation-defined*. If the
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| 170 |
+
attempt succeeds, the directive with the so-formed *header-name* is
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| 171 |
+
processed as specified for the previous form. Otherwise, the program is
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| 172 |
+
ill-formed.
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| 173 |
+
|
| 174 |
+
[*Note 2*: Adjacent *string-literal*s are not concatenated into a
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| 175 |
+
single *string-literal* (see the translation phases in [[lex.phases]]);
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| 176 |
+
thus, an expansion that results in two *string-literal*s is an invalid
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| 177 |
+
directive. — *end note*]
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| 178 |
+
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| 179 |
+
Any further processing as in normal text described for the previous form
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| 180 |
+
is not performed.
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| 181 |
+
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| 182 |
+
[*Note 3*: That is, processing as in normal text happens once and only
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| 183 |
+
once for the entire directive. — *end note*]
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| 184 |
+
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| 185 |
+
[*Example 4*:
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| 186 |
+
|
| 187 |
+
If the directive matches the second form, the whole directive is
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| 188 |
+
replaced. If the directive matches the first form, everything after the
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| 189 |
+
*header-name* is replaced.
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| 190 |
+
|
| 191 |
+
``` cpp
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| 192 |
+
#define EMPTY
|
| 193 |
+
#define X myfile
|
| 194 |
+
#define Y rsc
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| 195 |
+
#define Z 42
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| 196 |
+
#embed <myfile.rsc> prefix(Z)
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| 197 |
+
#embed EMPTY <X.Y> prefix(Z)
|
| 198 |
+
```
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| 199 |
+
|
| 200 |
+
is equivalent to:
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| 201 |
+
|
| 202 |
+
``` cpp
|
| 203 |
+
#embed <myfile.rsc> prefix(42)
|
| 204 |
+
#embed <myfile.rsc> prefix(42)
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| 205 |
+
```
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| 206 |
+
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| 207 |
+
— *end example*]
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| 208 |
+
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