我們已經(jīng)討論過(guò)了,在舊版本的 Fortran,有兩個(gè)實(shí)型類型:默認(rèn)的實(shí)型和雙精度型。
然而,F(xiàn)ortran語(yǔ)言90/95提供了更多通過(guò)種指定精度控制實(shí)數(shù)和整數(shù)數(shù)據(jù)類型。
不同類型的數(shù)字都在計(jì)算機(jī)內(nèi)部存儲(chǔ)方式不同。 kind屬性允許指定一個(gè)數(shù)字內(nèi)部存儲(chǔ)。例如,
real, kind = 2 :: a, b, c real, kind = 4 :: e, f, g integer, kind = 2 :: i, j, k integer, kind = 3 :: l, m, n
在上述聲明中,實(shí)際變量e,f和g 比實(shí)型變量 a,b 和 c 更精確。整數(shù)變數(shù)l,m 和 n,可以存儲(chǔ)較大的值,并有更多的存儲(chǔ)比整數(shù)變量I,J和k有更多位。雖然這是依賴于機(jī)器。
示例
program kindSpecifier implicit none real(kind = 4) :: a, b, c real(kind = 8) :: e, f, g integer(kind = 2) :: i, j, k integer(kind = 4) :: l, m, n integer :: kind_a, kind_i, kind_e, kind_l kind_a = kind(a) kind_i = kind(i) kind_e = kind(e) kind_l = kind(l) print *,'default kind for real is', kind_a print *,'default kind for int is', kind_i print *,'extended kind for real is', kind_e print *,'default kind for int is', kind_l end program kindSpecifier
當(dāng)編譯并執(zhí)行上述程序,將產(chǎn)生以下結(jié)果:
default kind for real is 4 default kind for int is 2 extended kind for real is 8 default kind for int is 4
有一些內(nèi)在的功能,用于詢問(wèn)數(shù)字的大小。
例如,bit_size(i)內(nèi)部函數(shù)指定用于存儲(chǔ)位數(shù)。對(duì)于實(shí)數(shù),precision(x)內(nèi)部函數(shù),返回小數(shù)位精度的數(shù)字,而range(x)內(nèi)部函數(shù)返回指數(shù)的十進(jìn)制范圍。
例子
program getSize implicit none real (kind = 4) :: a real (kind = 8) :: b integer (kind = 2) :: i integer (kind = 4) :: j print *,'precision of real(4) =', precision(a) print *,'precision of real(8) =', precision(b) print *,'range of real(4) =', range(a) print *,'range of real(8) =', range(b) print *,'maximum exponent of real(4) =' , maxexponent(a) print *,'maximum exponent of real(8) =' , maxexponent(b) print *,'minimum exponent of real(4) =' , minexponent(a) print *,'minimum exponent of real(8) =' , minexponent(b) print *,'bits in integer(2) =' , bit_size(i) print *,'bits in integer(4) =' , bit_size(j) end program getSize
當(dāng)編譯并執(zhí)行上述程序,將產(chǎn)生以下結(jié)果:
precision of real(4) = 6 precision of real(8) = 15 range of real(4) = 37 range of real(8) = 307 maximum exponent of real(4) = 128 maximum exponent of real(8) = 1024 minimum exponent of real(4) = -125 minimum exponent of real(8) = -1021 bits in integer(2) = 16 bits in integer(4) = 32
Fortran語(yǔ)言提供了兩個(gè)內(nèi)部函數(shù)來(lái)獲得類型值整數(shù)和實(shí)數(shù)的精度:
selected_real_kind函數(shù)返回一個(gè)整數(shù),一個(gè)給定的小數(shù)精度p 和十進(jìn)制指數(shù)范圍r 的類型的參數(shù)值。小數(shù)精度是明顯的位數(shù),而小數(shù)指數(shù)范圍規(guī)定的最小和最大可表示數(shù)。因此該范圍是從10-r 到 10+r。
例如,selected_real_kind (p = 10, r = 99) 返回所需的10精確到小數(shù)點(diǎn)后類型值,和一系列從10-99?10+99。
示例
program getKind implicit none integer:: i i = selected_real_kind (p = 10, r = 99)上一篇:Fortran算術(shù)運(yùn)算符下一篇:Fortran動(dòng)態(tài)數(shù)組