MATLAB Functions

Read formatted data from file

A = fscanf(fid,format)
[A,count] = fscanf(fid,format,size)

Description

A = fscanf(fid,format)

reads all the data from the file specified by fid, converts it according to the specified format string, and returns it in matrix A. Argument fid is an integer file identifier obtained from fopen. format is a string specifying the format of the data to be read. See "Remarks" for details.

[A,count] = fscanf(fid,format,size)

reads the amount of data specified by size, converts it according to the specified format string, and returns it along with a count of elements successfully read. size is an argument that determines how much data is read. Valid options are:




n 
Read n elements into a column vector.

inf 
Read to the end of the file, resulting in a column vector containing 
the same number of elements as are in the file.

[m,n] 
Read enough elements to fill an m-by-n matrix, filling the matrix in 
column order. n can be Inf, but not m.

`n`	Read `n` elements into a column vector.
`inf`	Read to the end of the file, resulting in a column vector containing the same number of elements as are in the file.
`[m,n]`	Read enough elements to fill an `m`-by-`n` matrix, filling the matrix in column order. `n` can be `Inf`, but not `m`.

fscanf differs from its C language namesakes scanf() and fscanf() in an important respect -- it is vectorized in order to return a matrix argument. The format string is cycled through the file until an end-of-file is reached or the amount of data specified by size is read in.

Remarks

When MATLAB reads a specified file, it attempts to match the data in the file to the format string. If a match occurs, the data is written into the matrix in column order. If a partial match occurs, only the matching data is written to the matrix, and the read operation stops.

The format string consists of ordinary characters and/or conversion specifications. Conversion specifications indicate the type of data to be matched and involve the character %, optional width fields, and conversion characters, organized as shown below:

Add one or more of these characters between the % and the conversion character:


An asterisk (*)	Skip over the matched value, if the value is matched but not stored in the output matrix.
A digit string	Maximum field width.
A letter	The size of the receiving object; for example, `h` for short as in `%hd` for a short integer, or `l` for long as in `%ld` for a long integer `or` `%lg` for a double floating-point number.

Valid conversion characters are:


`%c`	Sequence of characters; number specified by field width
`%d`	Decimal numbers
`%e, %f, %g`	Floating-point numbers
`%i`	Signed integer
`%o`	Signed octal integer
`%s`	A series of non-white-space characters
`%u`	Signed decimal integer
`%x`	Signed hexadecimal integer
`[...]`	Sequence of characters (scanlist)

If %s is used, an element read may use several MATLAB matrix elements, each holding one character. Use %c to read space characters; the format %s skips all white space.

Mixing character and numeric conversion specifications cause the resulting matrix to be numeric and any characters read to appear as their ASCII values, one character per MATLAB matrix element.

For more information about format strings, refer to the scanf() and fscanf() routines in a C language reference manual.

Examples

The example in fprintf generates an ASCII text file called exp.txt that looks like:

0.00    1.00000000
0.10    1.10517092
...
1.00    2.71828183

Read this ASCII file back into a two-column MATLAB matrix:

fid = fopen('exp.txt');
a = fscanf(fid,'%g %g',[2 inf]) % It has two rows now.
a = a';
fclose(fid)