matlab-控制文件读写位置及格式化读写ascii

help fseek
 FSEEK Set file position indicator.
    STATUS = FSEEK(FID, OFFSET, ORIGIN) repositions the file position
    indicator in the file associated with the given FID.  FSEEK sets the
    position indicator to the byte with the specified OFFSET relative to
    ORIGIN.
 
    FID is an integer file identifier obtained from FOPEN.
 
    OFFSET values are interpreted as follows:
        >= 0    Move position indicator OFFSET bytes after ORIGIN.
        < 0    Move position indicator OFFSET bytes before ORIGIN.
 
    ORIGIN values are interpreted as follows:
        'bof' or -1   Beginning of file
        'cof' or  0   Current position in file
        'eof' or  1   End of file
 
    STATUS is 0 on success and -1 on failure.  If an error occurs, use
    FERROR to get more information.
 
    Example:
 
        fseek(fid,0,-1)
 
    "rewinds" the file.

fseek用于定位

 1）读

 

>> fid=fopen('test.m','r')

fid =

     3

>> fseek(fid,5,'bof')

ans =

     0

>> a=fread(fid,5,'uint8=>char')

a =

1
 
0
 
;

>>

 

>> fseek(fid,0,'bof')

ans =

     0

>> a=fread(fid,5,'uint8=>char')

a =

P
=
[
1
 

>>

 

2)写

>> fid=fopen('test.m','r+')

fid =

     3

>> fseek(fid,0,'eof')

ans =

     0

>> fwrite(fid,'%增加一行','char')

ans =

     5

>> fclose(fid)

ans =

     0

>>

 

定位于当前位置写，注意这种写是改写

>> fid=fopen('test.m','r+')

fid =

     3

>> fseek(fid,0,'cof')

ans =

     0

>> ftell(fid)

ans =

     0

>> fwrite(fid,'%增加上面一行','char')

ans =

     7

>> fclose(fid)

ans =

     0

>>

 

ftell得到当前位置

 help ftell
 FTELL Get file position indicator.
    POSITION = FTELL(FID) returns the location of the file position
    indicator in the specified file.  Position is indicated in bytes
    from the beginning of the file.  If -1 is returned, it indicates
    that the query was unsuccessful. Use FERROR to determine the nature
    of the error.
 
    FID is an integer file identifier obtained from FOPEN.

 

 

3、读取行

1)fgetl

>> fid=fopen('test.m','r')

fid =

     4

>> mline=fgetl(fid)

mline =

%增加上面一行 1];

>> mline=fgetl(fid)

mline =

T=[0 1 0];

>> mline=fgetl(fid)

mline =

w=[0 0 ];

>> mline=fgetl(fid)

mline =

[S,Q]=size(T)

>> mline=fgetl(fid)

mline =

b=0;

>>

2)fgets

与fgetl的区别就是,fgets是保留换行符读取一行

>> mline=fgets(fid)

mline =

A=purelin(w*P+b);

 

>>

 

4、格式化读写ascii

1)读

>> a=fscanf(fid,'%s',10)

a =

e=T-A;LP.lr=maxlinlr(P)%误差平方和sse=sumsqr(e);whilesse>0.0000001dW=learnwh([],P,[],[],[],[],e,[],[],[],LP,[]);dB=learnwh(b,ones(1,Q),[],[],[],[],e,[],[],[],LP,[]);

>>

 

>> a=fscanf(fid,'%s')

a =

w=w+dW;b=b+dB;A=purelin(w*P+b)e=T-Asse=sumsqr(e)end%增加一行

>>

 

 help fscanf
 FSCANF Read formatted data from file.
    [A,COUNT] = FSCANF(FID,FORMAT,SIZE) reads data from the file specified
    by file identifier FID, converts it according to the specified FORMAT
    string, and returns it in matrix A. COUNT is an optional output
    argument that returns the number of elements successfully read.
   
    FID is an integer file identifier obtained from FOPEN.
   
    SIZE is optional; it puts a limit on the number of elements that
    can be read from the file; if not specified, the entire file
    is considered; if specified, valid entries are:
 
        N      read at most N elements into a column vector.
        inf    read at most to the end of the file.
        [M,N]  read at most M * N elements filling at least an
               M-by-N matrix, in column order. N can be inf, but not M.
 
    If the matrix A results from using character conversions only and
    SIZE is not of the form [M,N] then a row vector is returned.
 
    FORMAT is a string containing ordinary characters and/or C language
    conversion specifications. Conversion specifications involve the
    character %, optional assignment-suppressing asterisk and width
    field, and conversion characters d, i, o, u, x, e, f, g, s, c, and
    [. . .] (scanset). Complete ANSI C support for these conversion
    characters is provided consistent with 'expected' MATLAB behavior.
    For a complete conversion character specification, see the Language
    Reference Guide or a C manual.
 
    If %s is used an element read may cause several MATLAB matrix
    elements to be used, each holding one character.  Use %c to read
    space characters; the format %s skips all white space.
 
    MATLAB reads characters using the encoding scheme associated with
    the file. See FOPEN for more information. If the format string
    contains ordinary characters, MATLAB matches each of those characters
    with a character read from the file after converting both to the
    MATLAB internal representation of characters.
 
    Mixing character and numeric conversion specifications causes the
    resulting matrix to be numeric and any characters read to show up
    as their numeric values, one character per MATLAB matrix element.
 
    FSCANF differs from its C language namesake in an important respect -
    it is "vectorized" in order to return a matrix argument. The format
    string is recycled through the file until an end-of-file is reached
    or the amount of data specified by SIZE is read in.
 
    Examples:
        S = fscanf(fid,'%s')   reads (and returns) a character string.
        A = fscanf(fid,'%5d')  reads 5-digit decimal integers.

 

 

2)写

>> fid=fopen('test.m','r+')

fid =

     4

>> fseek(fid,0,'eof')

ans =

     0

>> x=[123,3452]

x =

         123        3452

>> fprintf(fid,'%d %6.2f',x)

ans =

    11

>> fclose(fid)

ans =

     0

>>

 

help fprintf
 FPRINTF Write formatted data to text file.
    FPRINTF(FID, FORMAT, A, ...) applies the FORMAT to all elements of
    array A and any additional array arguments in column order, and writes
    the data to a text file.  FID is an integer file identifier.  Obtain
    FID from FOPEN, or set it to 1 (for standard output, the screen) or 2
    (standard error). FPRINTF uses the encoding scheme specified in the
    call to FOPEN.
 
    FPRINTF(FORMAT, A, ...) formats data and displays the results on the
    screen.
 
    COUNT = FPRINTF(...) returns the number of bytes that FPRINTF writes.
 
    FORMAT is a string that describes the format of the output fields, and
    can include combinations of the following:
 
       * Conversion specifications, which include a % character, a
         conversion character (such as d, i, o, u, x, f, e, g, c, or s),
         and optional flags, width, and precision fields.  For more
         details, type "doc fprintf" at the command prompt.
 
       * Literal text to print.
 
       * Escape characacters, including:
             \b     Backspace            ''   Single quotation mark
             \f     Form feed            %%   Percent character
             \n     New line             \\   Backslash
             \r     Carriage return      \xN  Hexadecimal number N
             \t     Horizontal tab       \N   Octal number N
         For most cases, \n is sufficient for a single line break.
         However, if you are creating a file for use with Microsoft
         Notepad, specify a combination of \r\n to move to a new line.
 
    Notes:
 
    If you apply an integer or string conversion to a numeric value that
    contains a fraction, MATLAB overrides the specified conversion, and
    uses %e.
 
    Numeric conversions print only the real component of complex numbers.
 
    Example: Create a text file called exp.txt containing a short table of
    the exponential function.
 
        x = 0:.1:1;
        y = [x; exp(x)];
        fid = fopen('exp.txt','w');
        fprintf(fid,'%6.2f  %12.8f\n',y);
        fclose(fid);
 
    Examine the contents of exp.txt:
 
        type exp.txt
 
    MATLAB returns:
           0.00    1.00000000
           0.10    1.10517092
                ...
           1.00    2.71828183
 

 

 

最后是关闭文件

help fclose
 FCLOSE Close file.
    ST = FCLOSE(FID) closes the file associated with file identifier FID,
    which is an integer value obtained from an earlier call to FOPEN. 
    FCLOSE returns 0 if successful or -1 if not.  If FID does not represent
    an open file, or if it is equal to 0 (standard input), 1 (standard
    output), or 2 (standard error), FCLOSE throws an error.
 
    ST = FCLOSE('all') closes all open files, except 0, 1 and 2.
    See also fopen, fclose, fscanf, fread, fwrite, sprintf, disp.