[c1 c2 c3 c4] = textread('sample_file2.txt','%s %s %s %s','headerlines',2)，其中的headerlines是什么意思？還有，file = textread('fft.m','%s','delimiter','\n','whitespace','');其中的delimiter，whitespace有什么作用？
2 回答
ABOUTYOU
TA貢獻1812條經驗 獲得超5個贊
headerlines表示開頭跳過幾行(有的文件開頭有說明文字)
delimiter 設置分隔符,用來隔開多個數據,whitespace表示把這個字符作為空格來處理 區別是分隔符更嚴格,只要讀到這個字符,當前的這個數據就截止了,空格則不一定,具體情況自己試驗一下了
help里說的很詳細,懂英文的話自己看下
textread
Read data from text file; write to multiple outputs
Note textread is not recommended. Use textscan to read data from a text file.
Graphical Interface
As an alternative to textread, use the Import Wizard. To activate the Import Wizard, select Import Data from the File menu.
Syntax
[A,B,C,...] = textread('filename','format')
[A,B,C,...] = textread('filename','format',N)
[...] = textread(...,'param','value',...)
Description
[A,B,C,...] = textread('filename','format') reads data from the file 'filename' into the variables A,B,C, and so on, using the specified format, until the entire file is read. The filename and format inputs are strings, each enclosed in single quotes. textread is useful for reading text files with a known format. textread handles both fixed and free format files.
Note When reading large text files, reading from a specific point in a file, or reading file data into a cell array rather than multiple outputs, you might prefer to use the textscan function.
textread matches and converts groups of characters from the input. Each input field is defined as a string of non-white-space characters that extends to the next white-space or delimiter character, or to the maximum field width. Repeated delimiter characters are significant, while repeated white-space characters are treated as one.
The format string determines the number and types of return arguments. The number of return arguments is the number of items in the format string. The format string supports a subset of the conversion specifiers and conventions of the C language fscanf routine. Values for the format string are listed in the table below. White-space characters in the format string are ignored.
format
Action
Output
Literals
(ordinary characters)
Ignore the matching characters. For example, in a file that has Dept followed by a number (for department number), to skip the Dept and read only the number, use 'Dept' in the format string.
None
%d
Read a signed integer value.
Double array
%u
Read an integer value.
Double array
%f
Read a floating-point value.
Double array
%s
Read a white-space or delimiter-separated string.
Cell array of strings
%q
Read a double quoted string, ignoring the quotes.
Cell array of strings
%c
Read characters, including white space.
Character array
%[...]
Read the longest string containing characters specified in the brackets.
Cell array of strings
%[^...]
Read the longest nonempty string containing characters that are not specified in the brackets.
Cell array of strings
%*...
instead of %
Ignore the matching characters specified by *.
No output
%w...
instead of %
Read field width specified by w. The %f format supports %w.pf, where w is the field width and p is the precision.
[A,B,C,...] = textread('filename','format',N) reads the data, reusing the format string N times, where N is an integer greater than zero. If N is smaller than zero, textread reads the entire file.
[...] = textread(...,'param','value',...) customizes textread using param/value pairs, as listed in the table below.
param
value
Action
bufsize
Positive integer
Specifies the maximum string length, in bytes. Default is 4095.
commentstyle matlab
Ignores characters after %.
commentstyle shell
Ignores characters after #.
commentstyle c
Ignores characters between /* and */.
commentstyle c++
Ignores characters after //.
delimiter
One or more characters
Act as delimiters between elements. Default is none.
emptyvalue
Scalar double
Value given to empty cells when reading delimited files. Default is 0.
endofline
Single character or '\r\n'
Character that denotes the end of a line.
Default is determined from file
expchars
Exponent characters
Default is eEdD.
headerlines
Positive integer
Ignores the specified number of lines at the beginning of the file.
whitespace
Any from the list below:
Treats vector of characters as white space. Default is ' \b\t'.
' '
\b
\n
\r
\t
Space
Backspace
Newline
Carriage return
Horizontal tab
Note When textread reads a consecutive series of whitespace values, it treats them as one white space. When it reads a consecutive series of delimiter values, it treats each as a separate delimiter.
Remarks
If you want to preserve leading and trailing spaces in a string, use the whitespace parameter as shown here:
textread('myfile.txt', '%s', 'whitespace', '')
ans =
' An example of preserving spaces '
Examples
Example 1 — Read All Fields in Free Format File Using %
The first line of mydata.dat is
Sally Level1 12.34 45 Yes
Read the first line of the file as a free format file using the % format.
[names, types, x, y, answer] = textread('mydata.dat', ...
'%s %s %f %d %s', 1)
returns
names =
'Sally'
types =
'Level1'
x =
12.34000000000000
y =
45
answer =
'Yes'
Example 2 — Read as Fixed Format File, Ignoring the Floating Point Value
The first line of mydata.dat is
Sally Level1 12.34 45 Yes
Read the first line of the file as a fixed format file, ignoring the floating-point value.
[names, types, y, answer] = textread('mydata.dat', ...
'%9c %5s %*f %2d %3s', 1)
returns
names =
Sally
types =
'Level1'
y =
45
answer =
'Yes'
%*f in the format string causes textread to ignore the floating point value, in this case, 12.34.
Example 3 — Read Using Literal to Ignore Matching Characters
The first line of mydata.dat is
Sally Type1 12.34 45 Yes
Read the first line of the file, ignoring the characters Type in the second field.
[names, typenum, x, y, answer] = textread('mydata.dat', ...
'%s Type%d %f %d %s', 1)
returns
names =
'Sally'
typenum =
1
x =
12.34000000000000
y =
45
answer =
'Yes'
Type%d in the format string causes the characters Type in the second field to be ignored, while the rest of the second field is read as a signed integer, in this case, 1.
Example 4 — Specify Value to Fill Empty Cells
For files with empty cells, use the emptyvalue parameter. Suppose the file data.csv contains:
1,2,3,4,,6
7,8,9,,11,12
Read the file using NaN to fill any empty cells:
data = textread('data.csv', '', 'delimiter', ',', ...
'emptyvalue', NaN);
Example 5 — Read M-File into a Cell Array of Strings
Read the file fft.m into cell array of strings.
file = textread('fft.m', '%s', 'delimiter', '\n', ...
'whitespace', '');
紫衣仙女
TA貢獻1839條經驗 獲得超15個贊
一些低級的I/O處理及相關介紹
函數 功能
fclose 關閉打開的文件
feof 判斷是否為文件結尾
ferror 文件輸入輸出中的錯誤查找
fgetl 讀入一行，忽略換行符
fgets 讀入一行，直到換行符
fopen 打開文件，或者獲取打開文件的信息
fprintf 格式化輸入數據到文件
fread 從文件中讀取二進制數據
frewind 將文件的位置指針移至文件開頭位置
fscanf 格式化讀入
fseek 設置文件位置指針
ftell 文件位置指針
fwrite 向文件中寫入數據
下面重點介紹函數fprintf。該函數的調用格式如下：
count=fprintf(fid,format,A,...)，該語句將矩陣A及后面其他參數中數字的實部以format指定的格式寫入到fid指定的文件中，返回寫入數據的字節數。
上面語句中，參數format由%開頭，共可由4個部分組成，分別如下：
●標記(flag)，為可選部分。
●寬度和精度指示，為可選部分。
●類型標志符，為可選部分。
●轉換字符，為必需部分。
1.標記
標記用于控制輸出的對齊方式，可以選擇的內容如下
函數 功能 示例
負號(-) 在參數左側進行判別 %-5.2 d
加號(+) 在數字前添加符號 %+5.2 d
空格 在數字前插入空格 %5.2 d
0 在數字前插入0 %0 5.2 d
2.寬度和精度指示
用戶可以通過數字指定輸出數字的寬度及精度，格式如下：
●o，指定數字的寬度；
●%6.2f，指定數字的寬度及精度；
●%.2f，指定數字的精度。
3.轉換字符
轉換字符用于指定輸出的符號，可以選擇的內容如下
標志符 意義
%c 輸出單個字符
%d 輸出有符號十進制數
%e 采用指數格式輸出，采用小寫字母e，如：3.1415e+00
%E 采用指數格式輸出，采用大寫字母E，如：3.1415E+00
%f 以定點數的格式輸出
%g %e及%f 更緊湊的格式，不顯示數字中無效的0
%G與%g相同，但是使用大寫字母E
%i 有符號十進制數
%o 無符號八進制數
%s 輸出字符串
%u 無符號十進制數
%x 十六進制數(使用小寫字母a－f)
%X 十六進制數(使用大寫字母A－F)
其中%o、%u、%x、%X支持使用子類型。
例如：
例13-7 fprintf格式化輸出示例。
>>x=0:.1:1;
>>y=[x;exp(x)];
>>fid=fopen('exp.txt','wt');
>>fprintf(fid,'%6.2f.8f\n',y);
>>fclose(fid)
ans=
0
顯示該文件：
>>typeexp.txt
0.00 1.00000000
0.10 1.10517092
…
0.90 2.45960311
1.00 2.71828183
f p r i n t f(1,'It''s Friday.\n')
It's Friday. 在該例中，利用1表示顯示器，并且用兩個單引號顯示單引號，使用\n進行換行。在格式化輸出中，這類符號稱為轉義符。MATLAB中的常用轉義符如表下所示。
轉義符 功能
\b 退格
\f 表格填充
\n 換行符
\r 回車
\t t a b
\\ \，反斜線
\''或'' '，單引號
%% %，百分號
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