带有打印语句的整数输出格式 [英] Integer output formatting with print statement

问题描述

I've noted that if I use integer(16) variables, when I use print, the output contains the exact number of spaces expected. Thus, when I use (some might recognize a project euler problem here)

    implicit none
    integer(16)::sum_sq,sq_sum,diff,i
    sum_sq=0;sq_sum=0;
    do i=1,100
       sum_sq=sum_sq+i*i
       sq_sum=sq_sum+i
    enddo
    diff=abs(sq_sum**2-sum_sq)
    print *, "The difference is", diff

I get

The difference is 25164150

as the output, but when I use integer(8) or integer for the variables, I get

The difference is             25164150

as the output. This occurs with and without the -m64 flag and only on gfortran (my ifort does not seem to accept kind=16, a separate issue to be dealt with, but returns the output with the spaces for integer(8)).

Does anyone know why this occurs?

解决方案

As already answered, you are using list-directed IO, which while convenient, is not completely specified by the language standard. So you will find idiosyncrasies. If you want to control the output will need to use a format. Also convient is the format specifier "I0", which uses the minimum number of digits required to output the item.

As a side issue, "integer (N)" is not guaranteed to be an N-byte integer. It is not the same as "integer*N", which is not part of the language standard. Many compilers use for the kind values the number of bytes of the type, but there are exceptions. In hindsight, it was a mistake to use integer values to designate integer, real & logical sub-types. If you want to select types by the number of bytes, there are methods starting with Fortran 2003. The ISO_C_Binding module of Fortran 2003 provides type designators such as C_INT32_T, C_INT64_T and C_INT128_T. The ISO_FORTRAN_ENV module for Fortran 2008 provides INT8, INT16, INT32 and INT64.

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