GNU gperf

https://www.gnu.org/software/gperf/manual/html_node/
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GNU gperf is a perfect hash function generator that produces C or C++ lookup tables from a static...
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### Example keyword entries for C reserved words

Source: https://www.gnu.org/software/gperf/manual/html_node/Keywords.html

A simple example from a partial list of C reserved words. Lines starting with '#' are comments. Each non-comment line contains a keyword as the first field, with no leading whitespace.

```plaintext
# These are a few C reserved words, see the c.gperf file 
# for a complete list of ANSI C reserved words.
unsigned
sizeof
switch
signed
if
default
for
while
return

```

--------------------------------

### Minimal Keyword-Only Input Format

Source: https://www.gnu.org/software/gperf/manual/html_node/Input-Format.html

An example of an input file starting directly with keywords, which is possible when the '-t' option is omitted.

```text
january
february
march
april
...
```

--------------------------------

### Inserting GNU indent directives

Source: https://www.gnu.org/software/gperf/manual/html_node/Controls-for-GNU-indent.html

Example showing where to place '/* *INDENT-OFF* */' and '/* *INDENT-ON* */' comments to allow GNU indent to process a gperf input file correctly.

```c
/* *INDENT-OFF* */
declarations part 1
%{
/* *INDENT-ON* */
verbatim code
/* *INDENT-OFF* */
%}
declarations part 2
%%
keywords
%%
/* *INDENT-ON* */
functions
```

--------------------------------

### Include C code with %{ %} in gperf input

Source: https://www.gnu.org/software/gperf/manual/html_node/C-Code-Inclusion.html

Use left-justified %{ and %} to insert C source text verbatim into the generated output. The example includes an assert.h header, a comment, and a function declaration, followed by the gperf input structure and keyword list.

```gperf
%{
#include <assert.h>
/* This section of code is inserted directly into the output. */
int return_month_days (struct month *months, int is_leap_year);
%}
struct month { char *name; int number; int days; int leap_days; };
%%
january,   1, 31, 31
february,  2, 28, 29
march,     3, 31, 31
...
```

--------------------------------

### Abbreviated struct declaration with month data

Source: https://www.gnu.org/software/gperf/manual/html_node/User_002dsupplied-Struct.html

Example input file when the struct has already been declared in an include file. Uses an abbreviated form 'struct month;' followed by %% and the month list. The ellipsis (...) indicates omitted data in the source.

```gperf
struct month;
%%
january,   1, 31, 31
...

```

--------------------------------

### Full struct declaration with month data

Source: https://www.gnu.org/software/gperf/manual/html_node/User_002dsupplied-Struct.html

Example input file for gperf with -t option. Defines a struct month with fields name, number, days, leap_days, followed by a %% separator and a list of month entries. The first field must be named 'name' and be of type char * (or const char *) unless -P is used.

```gperf
struct month { char *name; int number; int days; int leap_days; };
%%
january,   1, 31, 31
february,  2, 28, 29
march,     3, 31, 31
april,     4, 30, 30
may,       5, 31, 31
june,      6, 30, 30
july,      7, 31, 31
august,    8, 31, 31
september, 9, 30, 30
october,  10, 31, 31
november, 11, 30, 30
december, 12, 31, 31

```

--------------------------------

### General gperf input file structure

Source: https://www.gnu.org/software/gperf/manual/html_node/Controls-for-GNU-indent.html

The standard structure of a gperf input file containing declarations, verbatim code, keywords, and functions.

```text
declarations part 1
%{
verbatim code
%}
declarations part 2
%%
keywords
%%
functions
```
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