@weintek/libc/stdio - JS Action/Object SDK

The @weintek/libc/stdio module is primarily utilized for reading and writing external files.

Note:

The modules under @weintek/libc (e.g., errno, stdio, string, unistd) are heavily influenced by the design of C standard library.
The module is availabe when JS object/action is run on Local HMI)

Examples

Create a file and write "Hello, World!"

const cstdio = await import('@weintek/libc/stdio');
const encoder = new TextEncoder();
const file = cstdio.fopen('USB1', '/test/hello.txt', 'w');
cstdio.fwrite(file, encoder.encode('Hello, World!').buffer);
cstdio.fclose(file);

Open a file and read its content

const cstdio = await import('@weintek/libc/stdio');
const decoder = new TextDecoder();
const buffer = new ArrayBuffer(1024);
const file = cstdio.fopen('USB1', '/test/hello.txt', 'r');
let length = cstdio.fread(file, buffer);
if (length > 0) {
    console.log(decoder.decode(new Int8Array(buffer, 0, length)));
}
cstdio.fclose(file);

Members

(static, constant) SEEK_CUR :Number

Argument to fseek indicating seeking from the current file position

Type:

Number

(static, constant) SEEK_END :Number

Argument to fseek indicating seeking from end of the file

Type:

Number

(static, constant) SEEK_SET :Number

Argument to fseek indicating seeking from beginning of the file

Type:

Number

Methods

(static) clearerr(file)

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method resets the error flags and the EOF indicator for the given file stream file.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to reset the error flags for.

(static) fclose(file)

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method closes the given file stream.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to close.

(static) feof(file) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method checks if the end of the given file stream has been reached.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to check.

Returns:

Nonzero value if the end of the stream has been reached, otherwise 0.

Type: Number

(static) ferror(file) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method checks the given stream for errors.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to check.

Returns:

Nonzero value if the file stream has errors occurred, 0 otherwise.

Type: Number

(static) fflush(file) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method writes any unwritten data from the stream's buffer to the associated output device.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to write out.

Returns:

Returns zero on success. Otherwise a negative value is returned and the error indicator of the file stream is set.

Type: Number

(static) fileno(file) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

This method examines the argument file and returns the integer file descriptor used to implement this file stream.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to examine.

Returns:

Returns the integer file descriptor associated with stream. Otherwise, returns -1 and getErrno can be used to identify the error.

Type: Number

(static) fopen(disk, filename, mode) → {module:@weintek/libc/stdio~FILE}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method opens a file indicated by disk and filename, and returns a file stream associated with that file. mode is used to determine the file access mode.

Note:

The number of files that can be opened simultaneously is limited to 100.

Parameters:

Name Type Description

disk

String

A string specifies the target disk. Acceptable values are SD, USB1 and USB2.

filename

String

A string specifies the file path.

mode

String

A string specifies the file access mode.

File access flags

File access mode string	Meaning	Explanation	Action if file already exists	Action if file does not exist
"r"	read	Open a file for reading	read from start	failure to open
"w"	write	Create a file for writing	destroy contents	create new
"a"	append	Append to a file	write to end	create new
"r+"	read extended	Open a file for read/write	read from start	error
"w+"	write extended	Create a file for read/write	destroy contents	create new
"a+"	append extended	Open a file for read/write	write to end	create new

Returns:

If successful, returns the new file stream. On error, an exception is thrown.

Type: module:@weintek/libc/stdio~FILE

(static) fread(file, buffer, positionopt, lengthopt) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method reads data into buffer from the given input stream file. The file position indicator for the stream is advanced by the number of characters read.

Parameters:

Name	Type	Attributes	Default	Description
`file`	module:@weintek/libc/stdio~FILE			The file stream to read.
`buffer`	ArrayBuffer			The buffer for storing data read from the file stream.
`position`	Number	<optional>	`0`	The position (in bytes) where to start storing the read data from.
`length`	Number	<optional>	`buffer_size - position`	The length (in bytes) of data to be read.

Returns:

The length (in bytes) of data read successfully, which may be less than length if an error or end-of-file condition occurs.

Type: Number

(static) fseek(file, offset, origin) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method sets the file position indicator for the file stream file to the value pointed to by offset.

Example

Set file position indicator to beginning of the file

cstdio.fseek(file, 0, cstdio.SEEK_SET);

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to modify.
`offset`	Number	Number of bytes to offset from `origin`.
`origin`	Number	Position used as reference for the `offset`. It is specified by one of the SEEK_CUR, SEEK_END, SEEK_SET.

Returns:

If successful, returns zero. Otherwise, returns a non-zero value and getErrno() can be used to identify the error.

Type: Number

(static) ftell(file) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method returns the file position indicator for the file stream file.

Parameters:

Name	Type	Description
`file`	module:@weintek/libc/stdio~FILE	The file stream to examine.

Returns:

If successful, returns file position indicator. Otherwise, returns -1 and getErrno() can be used to identify the error.

Type: Number

(static) fwrite(file, buffer, positionopt, lengthopt) → {Number}

Since:

EasyBuilder Pro V6.09.01

See:

cppreference.com

This method writes data from buffer to the output stream file. The file position indicator for the stream is advanced by the number of characters written.

Parameters:

Name	Type	Attributes	Default	Description
`file`	module:@weintek/libc/stdio~FILE			The file stream to write.
`buffer`	ArrayBuffer			The buffer containing the data to be written.
`position`	Number	<optional>	`0`	The position (in bytes) where to start extracting written data from.
`length`	Number	<optional>	`-1`	The length (in bytes) of data to be written.

Returns:

The length (in bytes) of data written successfully, which may be less than length if an error occurs.

Type: Number

Type Definitions

FILE

Each FILE object denotes an input/output stream. Each stream is associated with a file.

Instances of the FILE object are created by the fopen method.

All FILE objects are EventEmitters (v5.2.8).

Type:

Object