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This chapter is for programmers who wish to use Kpathsea. See section Introduction, for the conditions under which you may do so.

Programming overview

Aside from this manual, your best source of information is the source to the programs I've modified to use Kpathsea (see section Introduction). Of those, Dviljk is probably the simplest, and hence a good place to start. Xdvik adds VF support and the complication of X resources. Dvipsk adds the complication of its own config files. Web2c is source code I also maintain, so it uses Kpathsea rather straightforwardly, but is of course complicated by the Web to C translation. Finally, Kpsewhich is a small utility program whose sole purpose is to exercise the main path-searching functionality.

Beyond these examples, the `.h' files in the Kpathsea source describe the interfaces and functionality (and of course the `.c' files define the actual routines, which are the ultimate documentation). `pathsearch.h' declares the basic searching routine. `tex-file.h' and `tex-glyph.h' define the interfaces for looking up particular kinds of files. You may wish to use #include <kpathsea/kpathsea.h>, which includes every Kpathsea header.

The library provides no way for an external program to register new file types: `tex-file.[ch]' must be modified to do this. For example, Kpathsea has support for looking up Dvips config files, even though no program other than Dvips will likely ever want to do so. I felt this was acceptable, since along with new file types should also come new defaults in `texmf.cnf' (and its descendant `paths.h'), since it's simplest for users if they can modify one configuration file for all kinds of paths.

Kpathsea does not parse any formats itself; it barely opens any files. Its primary purpose is to return filenames. The GNU font utilities does contain libraries to read TFM, GF, and PK files, as do the programs above, of course.

Calling sequence

The typical way to use Kpathsea in your program goes something like this:

  1. Call kpse_set_program_name with argv[0] as the first argument; the second argument is a string or NULL. The second argument is used by Kpathsea as the program name for the .program feature of config files (see section Config files). If the second argument is NULL, the value of the first argument is used. This function must be called before any other use of the Kpathsea library. If necessary, kpse_set_program_name sets the global variables program_invocation_name and program_invocation_short_name. These variables are used in the error message macros defined in `kpathsea/lib.h'. It sets the global variable kpse_program_name to the program name it uses. It also initializes debugging options based on the environment variable KPATHSEA_DEBUG (if that is set). Finally, it sets the variables SELFAUTOLOC, SELFAUTODIR and SELFAUTOPARENT to the location, parent and grandparent directory of the executable, removing `.' and `..' path elements and resolving symbolic links. These are used in the default configuration file to allow people to invoke TeX from anywhere, specifically from a mounted CD-ROM. (You can use `--expand-var=\$SELFAUTOLOC', etc., to see the values finds.)
  2. The kpse_set_progname is deprecated. A call to kpse_set_progname with argv[0] is equivalent to a call of kpse_set_program_name with first argument argv[0] and second argument NULL. The function is deprecated because it cannot ensure that the .program feature of config files will always work (see section Config files).
  3. Set debugging options. See section Debugging. If your program doesn't have a debugging option already, you can define one and set kpathsea_debug to the number that the user supplies (as in Dviljk and Web2c), or you can just omit this altogether (people can always set KPATHSEA_DEBUG). If you do have runtime debugging already, you need to merge Kpathsea's options with yours (as in Dvipsk and Xdvik).
  4. If your program has its own configuration files that can define search paths, you should assign those paths to the client_path member in the appropriate element of the kpse_format_info array. (This array is indexed by file type; see `tex-file.h'.) See `resident.c' in Dvipsk for an example.
  5. Call kpse_init_prog (see `proginit.c'). It's useful for the DVI drivers, at least, but for other programs it may be simpler to extract the parts of it that actually apply. This does not initialize any paths, it just looks for (and sets) certain environment variables and other random information. (A search path is always initialized at the first call to find a file of that type; this eliminates much useless work, e.g., initializing the BibTeX search paths in a DVI driver.)
  6. The routine to actually find a file of type format is kpse_find_format, defined in `tex-file.h'. These are macros that expand to a call to `kpse_find_file'. You can call, say, kpse_find_tfm after doing only the first of the initialization steps above--Kpathsea automatically reads the `texmf.cnf' generic config files, looks for environment variables, and does expansions at the first lookup.
  7. To find PK and/or GF bitmap fonts, the routines are kpse_find_pk, kpse_find_gf and kpse_find_glyph, defined in `tex-glyph.h'. These return a structure in addition to the resultant filename, because fonts can be found in so many ways. See the documentation in the source.
  8. To actually open a file, not just return a filename, call kpse_open_file. This function takes the name to look up and a Kpathsea file format as arguments, and returns the usual FILE *. It always assumes the file must exist, and thus will search the disk if necessary (unless the search path specified `!!', etc.). In other words, if you are looking up a VF or some other file that need not exist, don't use this.

Kpathsea also provides many utility routines. Some are generic: hash tables, memory allocation, string concatenation and copying, string lists, reading input lines of arbitrary length, etc. Others are filename-related: default path, tilde, and variable expansion, stat calls, etc. (Perhaps someday I'll move the former to a separate library.)

The `c-*.h' header files can also help your program adapt to many different systems. You will almost certainly want to use Autoconf for configuring your software if you use Kpathsea; I strongly recommend using Autoconf regardless. It is available from ftp://prep.ai.mit.edu/pub/gnu/.

Program-specific files

Many programs will need to find some configuration files. Kpathsea contains some support to make it easy to place them in their own directories. The Standard TeX directory structure (see section `Introduction' in A Directory Structure for TeX files), specifies that such files should go into a subdirectory named after the program, like `texmf/ttf2pk'.

Two special formats, `kpse_program_text_format' and `kpse_program_binary_format' exist, which use .:$TEXMF/program// as their compiled-in search path. To override this default, you can use the variable PROGRAMINPUTS in the environment and/or `texmf.cnf'. That is to say, the name of the variable is constructed by converting the name of the program to upper case, and appending INPUTS.

The only difference between these two formats is whether kpse_open_file will open the files it finds in text or binary mode.

Programming with config files

You can (and probably should) use the same texmf.cnf configuration file that Kpathsea uses for your program. This helps installers by keeping all configuration in one place.

To retrieve a value var from config files, the best way is to call kpse_var_value on the string var. This will look first for an environment variable var, then a config file value. The result will be the value found or `NULL'. This function is declared in `kpathsea/variable.h'. For an example, see the shell_escape code in `web2c/lib/texmfmp.c'.

The routine to do variable expansion in the context of a search path (as opposed to simply retrieving a value) is kpse_var_expand, also declared in `kpathsea/variable.h'. It's generally only necessary to set the search path structure components as explained in the previous section, rather than using this yourself.

If for some reason you want to retrieve a value only from a config file, not automatically looking for a corresponding environment variable, call kpse_cnf_get (declared in `kpathsea/cnf.h') with the string var.

No initialization calls are needed.

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