c ++中的指针?? [英] pointers in c++ ??
问题描述
我有一段用C ++实现FFT算法的代码，我需要将它转换成java。我试图理解
这些指针。任何有java和C ++经验的人，你能否请b / b
解释下面的代码，特别是a1 + = nFFT2行（我知道它是
增加a1变量/指针nFFT2但是如何给出每个数组的新元素
方法。任何能够将b $ b $翻译成java的人都会成为明星！
Cormac。
nFrames = 249;
nFFT2 = 128;
nChn = 25;
float * s = new float [nFrames * nFFT2]; // FFT
float * u = new float [nFrames * nChn]; // FB
// s你在这里对它们进行了操作
a1 = s;
float * a2 = u;
for（int i = 0; i< nFrames; i ++）{
FBFilter（a1，a2）;
a1 + = nFFT2;
a2 + = nChn;
}
Cormac O' 'Donnell写道：
我有一段代码在c ++中实现FFT算法，我必须将它转换为java 。我正试图理解这些指针。任何有java和C ++经验的人，你能不能解释下面的代码，
我不懂Java，但是C ++，所以也许我仍然可以帮忙。
尤其是a1 + = nFFT2行（我知道它增加了a1变量/指针
nFFT2但是它如何给每个数组的方法提供了新的元素）。
a1首先指向
nFrames * nFFT2元素数组的第一个元素。增加指针意味着让它指向下一个元素
，例如添加10对它意味着让它进一步指向10
元素。所以在第一次迭代中，函数得到一个指向第一个元素的指针，第二个是指向第128个元素的指针，然后指向第256个元素。上。我猜FBFilter将永远
占用128个元素。
任何能将这个转换成java的人都会成为明星!!!
Cormac。
nFrames = 249;
nFFT2 = 128;
nChn = 25;
浮动* s =新浮点数[nFrames * nFFT2] ; // FFT
float * u = new float [nFrames * nChn]; // FB
//你在这里对它们进行了操作
a1 = s;
float * a2 = u;
for（ int i = 0; i< nFrames; i ++）{
FBFilter（a1，a2）;
a1 + = nFFT2;
a2 + = nChn;
}
-
大小（字节）：141,067
（下载Microsoft DirectX 8 SDK页面。）
" Cormac O''Donnell" <共************ @ hotmail.com>在消息中写道
news：26 ************************* @ posting.google.co m ... < blockquote class =post_quotes>
我有一段用c ++实现FFT算法的代码，我必须把它转换成java。我正试图理解这些指针。任何有java和C ++经验的人，你能不能解释下面的代码，特别是a1 + = nFFT2行（我知道它会增加a1变量/指针nFFT2但是它如何给出<每个数组都有新的FBFilter元素。任何能够将其翻译成java的人都会成为明星！
Cormac。
nFrames = 249;
nFFT2 = 128;
nChn = 25;
float * s = new float [nFrames * nFFT2]; // FFT
float * u = new float [nFrames * nChn]; // FB
//你在这里对它们进行了操作
a1 = s;
float * a2 = u;
for（ int i = 0; i< nFrames; i ++）{
FBFilter（a1，a2）;
a1 + = nFFT2;
a2 + = nChn;
}
指针在这里使用的方式是毫无意义的（请原谅双关语。）
也许你会发现这个等价的代码更容易理解。
nFrames = 249;
nFFT2 = 128;
nChn = 25;
浮动* s = new float [nFrames * nFFT2]; // FFT
float * u = new float [nFrames * nChn]; // FB
// s你在这里对它们进行了操作
int i1 = 0;
int i2 = 0;
for（int i = 0; i< nFrames; i ++）{
FBFilter（& s [i1]，& u [i2} ]）;
i1 + = nFFT2;
i2 + = nChn;
}
它'真的那么简单。
john
" Cormac O'Donnell" <共************ @ hotmail.com>写了
我有一段用c ++实现FFT算法的代码，我必须把它转换成java。我正试图理解这些指针。任何有java和C ++经验的人，你能不能解释下面的代码，特别是a1 + = nFFT2行（我知道它会增加a1变量/指针nFFT2但是它如何给出<每个数组都有新的FBFilter元素。任何能够将这个翻译成java的人都会成为明星！
从实际的角度来看，为什么你不打包带有JNI
接口的C ++代码？这样，你就不需要付出努力来翻译它了。你的
FFT并没有突然变成一个慢速傅里叶变换。
Claudio Puviani
hi,
I have a piece of code implementing the FFT algorithm in c++ and i
have to convert it into java. i am getting stuck trying to understand
these pointers. Anyone who has experience in java and C++, could you
please explain the code below , esp the lines a1+=nFFT2( i know it
increments the a1 variable/pointer by nFFT2 but how does this give the
methos FBFilter new elements of each array). Anyone who could
translate this to java would be a star!!!
Cormac.
nFrames = 249;
nFFT2 = 128;
nChn =25;
float* s=new float[nFrames*nFFT2]; // FFT
float* u=new float[nFrames*nChn]; // FB
// s and u have operations done on them here
a1=s;
float* a2=u;
for(int i=0;i<nFrames;i++) {
FBFilter(a1,a2);
a1+=nFFT2;
a2+=nChn;
}
Cormac O''Donnell wrote:
hi,
I have a piece of code implementing the FFT algorithm in c++ and i
have to convert it into java. i am getting stuck trying to understand
these pointers. Anyone who has experience in java and C++, could you
please explain the code below ,
I don''t know Java, but C++, so maybe I can still help.
esp the lines a1+=nFFT2( i know it increments the a1 variable/pointer
by nFFT2 but how does this give the methos FBFilter new elements of
each array).
a1 starts with pointing to the first element of an array of
nFrames*nFFT2 elements. Incrementing a pointer means letting it point
to the next element, adding e.g. 10 to it means letting it point 10
elements further. So in the first iteration, the function gets a
pointer to the first element, in the second one, a pointer to the 128th
element, then to the 256th and so on. I guess that FBFilter will always
take a block of 128 elements.
Anyone who could translate this to java would be a star!!!
Cormac.
nFrames = 249;
nFFT2 = 128;
nChn =25;
float* s=new float[nFrames*nFFT2]; // FFT
float* u=new float[nFrames*nChn]; // FB
// s and u have operations done on them here
a1=s;
float* a2=u;
for(int i=0;i<nFrames;i++) {
FBFilter(a1,a2);
a1+=nFFT2;
a2+=nChn;
}
--
Size (bytes): 141,067
(Download page of Microsoft DirectX 8 SDK.)
"Cormac O''Donnell" <co************@hotmail.com> wrote in message
news:26*************************@posting.google.co m...hi,
I have a piece of code implementing the FFT algorithm in c++ and i
have to convert it into java. i am getting stuck trying to understand
these pointers. Anyone who has experience in java and C++, could you
please explain the code below , esp the lines a1+=nFFT2( i know it
increments the a1 variable/pointer by nFFT2 but how does this give the
methos FBFilter new elements of each array). Anyone who could
translate this to java would be a star!!!
Cormac.
nFrames = 249;
nFFT2 = 128;
nChn =25;
float* s=new float[nFrames*nFFT2]; // FFT
float* u=new float[nFrames*nChn]; // FB
// s and u have operations done on them here
a1=s;
float* a2=u;
for(int i=0;i<nFrames;i++) {
FBFilter(a1,a2);
a1+=nFFT2;
a2+=nChn;
}
The way pointers are being used here is pretty pointless (pardon the pun).
Perhaps you''ll find this equivalent code easier to understand.
nFrames = 249;
nFFT2 = 128;
nChn =25;
float* s=new float[nFrames*nFFT2]; // FFT
float* u=new float[nFrames*nChn]; // FB
// s and u have operations done on them here
int i1=0;
int i2=0;
for(int i=0;i<nFrames;i++) {
FBFilter(&s[i1],&u[i2]);
i1+=nFFT2;
i2+=nChn;
}
It''s really that simple.
john
"Cormac O''Donnell" <co************@hotmail.com> wrotehi,
I have a piece of code implementing the FFT algorithm in c++ and i
have to convert it into java. i am getting stuck trying to understand
these pointers. Anyone who has experience in java and C++, could you
please explain the code below , esp the lines a1+=nFFT2( i know it
increments the a1 variable/pointer by nFFT2 but how does this give the
methos FBFilter new elements of each array). Anyone who could
translate this to java would be a star!!!
From a practical point of view, why don''t you just wrap the C++ code with a JNI
interface? That way, you don''t need to put effort into translating it AND your
FFT doesn''t suddenly become a S L O W Fourier Transform.
Claudio Puviani
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