Fortran - 双精度问题
我有一个小程序，可以从二进制文件中读取一些数据并将其存储到普通（未格式化）文件中。这是来源：
Program calki2e
IMPLICIT NONE
!
DOUBLE PRECISION VAL
INTEGER P,Q,R,S
INTEGER IREC2C
PARAMETER( IREC2C=15000)
INTEGER AND,RSHIFT,LABEL,IMBABS,NX,IB,NFT77
INTEGER IND
DIMENSION IND(IREC2C)
DOUBLE PRECISION XP
DIMENSION XP(IREC2C)
CHARACTER(LEN=12) :: FN77 = 'input08'
CONTINUE
NFT77=77
!----------------------------------------------------------------------
2 CONTINUE
c
open(unit=NFT77,file=FN77,STATUS='OLD',
+ACCESS='SEQUENTIAL',FORM='UNFORMATTED')
open(unit=13,file='calki2e.txt')
REWIND(77)
4100 continue
READ(77) NX,IND,XP
IMBABS=IABS(NX)
DO 100 IB=1,IMBABS
LABEL=IND(IB)
P= AND(RSHIFT(LABEL, 24),255)
Q= AND(RSHIFT(LABEL, 16),255)
R= AND(RSHIFT(LABEL, 8),255)
S= AND( LABEL ,255)
VAL=XP(ib)
IF(P.EQ. Q) VAL=VAL+VAL
IF(R .EQ. S) VAL=VAL+VAL
IF((P .EQ. R).AND.(Q .EQ. S)) VAL=VAL+VAL
write(13,*)P,Q,R,S,val
100 CONTINUE
IF (NX.GT.0) GOTO 4100
CRB
CLOSE(UNIT=NFT77)
!
END
当我使用 gfortran 编译它时，我在输出文件中获得双精度，但使用 g77 我只获得单精度。出了什么问题以及如何更改？
I have a small program that read some data from binary file and stores it into normal (unformatted) files. Here is the source:
Program calki2e
IMPLICIT NONE
!
DOUBLE PRECISION VAL
INTEGER P,Q,R,S
INTEGER IREC2C
PARAMETER( IREC2C=15000)
INTEGER AND,RSHIFT,LABEL,IMBABS,NX,IB,NFT77
INTEGER IND
DIMENSION IND(IREC2C)
DOUBLE PRECISION XP
DIMENSION XP(IREC2C)
CHARACTER(LEN=12) :: FN77 = 'input08'
CONTINUE
NFT77=77
!----------------------------------------------------------------------
2 CONTINUE
c
open(unit=NFT77,file=FN77,STATUS='OLD',
+ACCESS='SEQUENTIAL',FORM='UNFORMATTED')
open(unit=13,file='calki2e.txt')
REWIND(77)
4100 continue
READ(77) NX,IND,XP
IMBABS=IABS(NX)
DO 100 IB=1,IMBABS
LABEL=IND(IB)
P= AND(RSHIFT(LABEL, 24),255)
Q= AND(RSHIFT(LABEL, 16),255)
R= AND(RSHIFT(LABEL, 8),255)
S= AND( LABEL ,255)
VAL=XP(ib)
IF(P.EQ. Q) VAL=VAL+VAL
IF(R .EQ. S) VAL=VAL+VAL
IF((P .EQ. R).AND.(Q .EQ. S)) VAL=VAL+VAL
write(13,*)P,Q,R,S,val
100 CONTINUE
IF (NX.GT.0) GOTO 4100
CRB
CLOSE(UNIT=NFT77)
!
END
When I compile it using gfortran I obtain double precision in output file but with g77 I get only single precision. What it wrong and how to change it?
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评论（4）
您的意思是“write (13, *) 语句吗？这是“列表定向”输出。它是一种方便的 I/O，几乎没有规则——您得到的结果将取决于编译器——它最适合用于调试和“快速而肮脏”的程序。要可靠地获取双精度的所有数字，请更改为格式化输出语句，指定您需要的位数（无论如何，最好切换到 gfortran，因为 g77 不再适用。发展。）
Do you mean the "write (13, *) statement. This is "list directed" output. It is a convenience I/O with few rules -- what you get will depend upon the compiler -- it is best used for debugging and "quick and dirty" programs. To reliably get all the digits of double precision, change to a formatted output statement, specifying the number of digits that you need. (It is probably best to switch to gfortran anyway, as g77 is no longer under development.)
您的数字是双精度的，但您以自由格式打印它们。您必须指定明确的格式
your numbers are double precision but you are printing them in free format. You have to specify an explicit format
如果您想保留代码 F77，请尝试类似
“1X”表示 1 个空格，“4I7”表示 4 个七宽度整数，1E14.10 表示 1 个 14 个字符宽度的科学记数法实数，具有 10 个有效数字。请随意修改数字以使其看起来正确。
这是一个关于该主题的非常好的教程。
If you want to keep your code F77, try something like
The "1X"s mean one space, "4I7" means four seven-width integers, and 1E14.10 means one fourteen-charater width scientific-notation real number with 10 significant digits. Feel free to mess around with the numbers to get it to look right.
This is a pretty good tutorial on the topic.
我很想将 write 语句上的格式设置为明确的格式，而不是在 write(13,*)P,Q,R,S,val 中使用
* 。I would be tempted to set the format on your write statement to something explicit, rather than use
* in write(13,*)P,Q,R,S,val.