Files (Asymptote: the Vector Graphics Language)

Next: Variable initializers, Previous: Deferred drawing, Up: Programming [Contents][Index]

6.7 Files ¶

Asymptote can read and write text files (including comma-separated value) files and portable XDR (External Data Representation) binary files.

An input file can be opened with

input(string name="", bool check=true, string comment="#", string mode="");

reading is then done by assignment:

file fin=input("test.txt");
real a=fin;

If the optional boolean argument check is false, no check will be made that the file exists. If the file does not exist or is not readable, the function bool error(file) will return true. The first character of the string comment specifies a comment character. If this character is encountered in a data file, the remainder of the line is ignored. When reading strings, a comment character followed immediately by another comment character is treated as a single literal comment character. If Asymptote is compiled with support for libcurl, name can be a URL.

Unless the -noglobalread command-line option is specified, one can change the current working directory for read operations to the contents of the string s with the function string cd(string s), which returns the new working directory. If string s is empty, the path is reset to the value it had at program startup.

When reading pairs, the enclosing parenthesis are optional. Strings are also read by assignment, by reading characters up to but not including a newline. In addition, Asymptote provides the function string getc(file) to read the next character (treating the comment character as an ordinary character) and return it as a string.

A file named name can be open for output with

file output(string name="", bool update=false, string comment="#", string mode="");

If update=false, any existing data in the file will be erased and only write operations can be used on the file. If update=true, any existing data will be preserved, the position will be set to the end-of-file, and both reading and writing operations will be enabled. For security reasons, writing to files in directories other than the current directory is allowed only if the -globalwrite (or -nosafe) command-line option is specified. Reading from files in other directories is allowed unless the -noglobalread command-line option is specified. The function string mktemp(string s) may be used to create and return the name of a unique temporary file in the current directory based on the string s.

There are two special files: stdin, which reads from the keyboard, and stdout, which writes to the terminal. The implicit initializer for files is null.

Data of a built-in type T can be written to an output file by calling one of the functions

write(string s="", T x, suffix suffix=endl ... T[]);
write(file file, string s="", T x, suffix suffix=none ... T[]);
write(file file=stdout, string s="", explicit T[] x ... T[][]);
write(file file=stdout, T[][]);
write(file file=stdout, T[][][]);
write(suffix suffix=endl);
write(file file, suffix suffix=none);

If file is not specified, stdout is used and terminated by default with a newline. If specified, the optional identifying string s is written before the data x. An arbitrary number of data values may be listed when writing scalars or one-dimensional arrays. The suffix may be one of the following: none (do nothing), flush (output buffered data), endl (terminate with a newline and flush), newl (terminate with a newline), DOSendl (terminate with a DOS newline and flush), DOSnewl (terminate with a DOS newline), tab (terminate with a tab), or comma (terminate with a comma). Here are some simple examples of data output:

file fout=output("test.txt");
write(fout,1);                  // Writes "1"
write(fout, endl);              // Writes a new line
write(fout,"List: ",1,2,3);     // Writes "List: 1     2     3"

A file may be opened with mode="xdr", to read or write double precision (64-bit) reals and single precision (32-bit) integers in Sun Microsystem’s XDR (External Data Representation) portable binary format (available on all UNIX platforms). Alternatively, a file may also be opened with mode="binary" to read or write double precision reals and single precision integers in the native (nonportable) machine binary format, or to read the entire file into a string. The virtual member functions file singlereal(bool b=true) and file singleint(bool b=true) be used to change the precision of real and integer I/O operations, respectively, for an XDR or binary file f. Similarly, the function file signedint(bool b=true) can be used to modify the signedness of integer reads and writes for an XDR or binary file f.

The virtual members name, mode, singlereal, singleint, and signedint may be used to query the respective parameters for a given file.

One can test a file for end-of-file with the boolean function eof(file), end-of-line with eol(file), and for I/O errors with error(file). One can flush the output buffers with flush(file), clear a previous I/O error with clear(file), and close the file with close(file). The function int precision(file file=stdout, int digits=0) sets the number of digits of output precision for file to digits, provided digits is nonzero, and returns the previous precision setting. The function int tell(file) returns the current position in a file relative to the beginning. The routine seek(file file, int pos) can be used to change this position, where a negative value for the position pos is interpreted as relative to the end-of-file. For example, one can rewind a file file with the command seek(file,0) and position to the final character in the file with seek(file,-1). The command seekeof(file) sets the position to the end of the file.

Assigning settings.scroll=n for a positive integer n requests a pause after every n output lines to stdout. One may then press Enter to continue to the next n output lines, s followed by Enter to scroll without further interruption, or q followed by Enter to quit the current output operation. If n is negative, the output scrolls a page at a time (i.e. by one less than the current number of display lines). The default value, settings.scroll=0, specifies continuous scrolling.

The routines

string getstring(string name="", string default="", string prompt="",
                 bool store=true);
int getint(string name="", int default=0, string prompt="",
           bool store=true);
real getreal(string name="", real default=0, string prompt="",
             bool store=true);
pair getpair(string name="", pair default=0, string prompt="",
             bool store=true);
triple gettriple(string name="", triple default=(0,0,0), string prompt="",
                 bool store=true);

defined in the module plain may be used to prompt for a value from stdin using the GNU readline library. If store=true, the history of values for name is stored in the file ".asy_history_"+name (see history). The most recent value in the history will be used to provide a default value for subsequent runs. The default value (initially default) is displayed after prompt. These functions are based on the internal routines

string readline(string prompt="", string name="", bool tabcompletion=false);
void saveline(string name, string value, bool store=true);

Here, readline prompts the user with the default value formatted according to prompt, while saveline is used to save the string value in a local history named name, optionally storing the local history in a file ".asy_history_"+name.

The routine history(string name, int n=1) can be used to look up the n most recent values (or all values up to historylines if n=0) entered for string name. The routine history(int n=0) returns the interactive history. For example,

write(output("transcript.asy"),history());

outputs the interactive history to the file transcript.asy.

The function int delete(string s) deletes the file named by the string s. Unless the -globalwrite (or -nosafe) option is enabled, the file must reside in the current directory. The function int rename(string from, string to) may be used to rename file from to file to. Unless the -globalwrite (or -nosafe) option is enabled, this operation is restricted to the current directory. The functions

int convert(string args="", string file="", string format="");
int animate(string args="", string file="", string format="");

call the ImageMagick commands magick and animate, respectively, with the arguments args and the file name constructed from the strings file and format.