使用铸造空指针的问题 [英] Problem on using a casted void pointer

问题描述

我有一个无效指针，我在使用前将其转换为适当的已知类型

。我投下这个无效*的类型来自英特尔的开源计算机视觉库

。这是我的非工作代码：


CvMat * rowVect = cvCreateMat（1，nfeatures，CV_MAKETYPE（images [0] -

> depth，1））;

// rowVect是指向CvMat类型的指针


cvReshape（images [0]，rowVect，0,1） ; //矢量化图像; readrow

是一个1xN矩阵（向量）

void * ptr;


switch（images [0] - >深度）

{

case IPL_DEPTH_8U：

ptr =（unsigned char *）rowVect-> data.ptr; // ptr定义为

unsigned char指针

break; //

数据是''union''类型


case IPL_DEPTH_8S：

ptr =（signed char *）rowVect- > data.ptr;

break;


case IPL_DEPTH_16S：

ptr =（unsigned short *）rowVect-> data.ptr;

break;


case IPL_DEPTH_32S：

ptr =（int *）rowVect-> data.i ; //我被定义为一个int指针

break;


case IPL_DEPTH _32F：

ptr =（float *）rowVect - > data.fl; // fl定义为float

指针

break;


case IPL_DEPTH_64F：

ptr =（double *）rowVect-> data.db; // db是一个双$

休息;


}


int i = 0，k;

while（i< nsamples）

{

cvReshape（images [i]，readrow，0,1）;

for（k = 0; k
Data-> data.db [i *（Data-> width）+ k] =（double）ptr [k]; //错误发生

这里

//填写数据矩阵

i ++;

}


错误：1）''void *''：未知大小

2）''typecast''：无法从void转换为double

>
im抱歉，如果在这里指向第三方图书馆是违法的，但它还是用标准C写的
但我的问题是纯粹的C

语言我想的问题。我投了无效指针，但后来我无法使用

它...


问候

解决方案

9月23日晚上7:14，kkirtac< kadir.kir ... @ gmail.comwrote：

我有一个无效指针，我在使用前将其转换为适当的已知类型

。我投下这个无效*的类型来自英特尔的开源计算机视觉库

。这是我的非b / b $ b b工作代码：


CvMat * rowVect = cvCreateMat（1，nfeatures，CV_MAKETYPE（images [0] - > depth ，1））;


// rowVect是指向CvMat类型的指针


cvReshape（images [0]，rowVect，0,1 ）; //矢量化图像; readrow

是一个1xN矩阵（向量）

void * ptr;


switch（images [0] - >深度）

{

case IPL_DEPTH_8U：

ptr =（unsigned char *）rowVect-> data.ptr; // ptr定义为

unsigned char指针

break; //

数据是''union''类型


case IPL_DEPTH_8S：

ptr =（signed char *）rowVect- > data.ptr;

break;


case IPL_DEPTH_16S：

ptr =（unsigned short *）rowVect-> data.ptr;

break;


case IPL_DEPTH_32S：

ptr =（int *）rowVect-> data.i ; //我被定义为一个int指针

break;


case IPL_DEPTH _32F：

ptr =（float *）rowVect - > data.fl; // fl定义为float

指针

break;


case IPL_DEPTH_64F：

ptr =（double *）rowVect-> data.db; // db是一个双$

休息;


}


int i = 0，k;

while（i< nsamples）

{

cvReshape（images [i]，readrow，0,1）;

for（k = 0; k
Data-> data.db [i *（Data-> width）+ k] =（double）ptr [k]; //错误发生

这里

//填写数据矩阵

i ++;

}


错误：1）''void *''：未知大小

2）''typecast''：无法从void转换为double

>
im抱歉，如果在这里指向第三方图书馆是违法的，但它还是用标准C写的
但我的问题是纯粹的C

语言我想的问题。我投了无效指针，但后来我无法使用

它...


问候

尝试重写（双）ptr [k]为（（double *）ptr）[k]


问候，

B. br />

9月23日下午12:50，boroph ... @ gmail.com写道：

9月23日晚上7:14，kkirtac< kadir.kir ... @ gmail.comwrote：

我有一个无效指针和在使用之前，我将其转换为适当的已知类型

。我投下这个无效*的类型来自英特尔的开源计算机视觉库

。这是我的非工作代码：

CvMat * rowVect = cvCreateMat（1，nfeatures，CV_MAKETYPE（图像[0] - >深度，1））;

// rowVect是指向CvMat类型的指针

cvReshape （images [0]，rowVect，0,1）; //矢量化图像; readrow

是1xN矩阵（向量）

void * ptr;

switch（images [0] - > depth）

{

case IPL_DEPTH_8U ：

ptr =（unsigned char *）rowVect-> data.ptr; // ptr定义为

unsigned char指针

break; //

数据是''union''类型

case IPL_DEPTH_8S：

ptr =（signed char *）rowVect-> data.ptr;

break;

case IPL_DEPTH_16S：

ptr =（unsigned short *）rowVect-> data.ptr;

休息;

case IPL_DEPTH_32S：

ptr =（int *）rowVect-> data.i; //我被定义为一个int指针

break;

case IPL_DEPTH _32F：

ptr =（float *）rowVect-> data.fl; // fl定义为float

指针

break;

case IPL_DEPTH_64F：

ptr =（double *）rowVect-> data.db; // db是双$
休息;

}

int i = 0，k;

while（i< nsamples）

{

cvReshape（images [i]，readrow，0,1）;

for（k = 0; k
Data-> data.db [i *（Data-> width）+ k] =（double）ptr [k]; //错误发生

这里

//填写数据矩阵

i ++;

}

错误：1）''void *''：未知大小

2）''typecast''：无法从void转换为double

im抱歉，如果将第三方库指向此处是违法的，那么

也是用标准编写的C.但我的问题是纯粹的C

语言。我想的问题。我投了一个无效指针，但后来我无法使用

它...

问候

尝试重写（双）ptr [k]为（（double *）ptr）[k]


问候，

B.

嗯，谢谢你，但问题是，如果我们在

ptr前设置一个双*，那么它会读取对应于''double''类型的字节数。

我想在这里做的是决定字节数（

将在前面的类型） ''ptr''）在上面''switch-case''语句中

一次，并在每次迭代中读取该字节数，将其转换为

double类型。例如，如果switch-case决定ptr将是
一个unsigned char *，那么而不是while循环中的double *，$
想要unsigned char *放在那里，然后将结果转换为

像这样：（double）（（unsigned char *）ptr）[k]。但问题是

i希望这会自动发生..我不想在while循环中运行

switch-case来决定那个......对不起，如果这个

太复杂了..

问候

kkirtac写道：
< blockquote class =post_quotes>
>

嗯，谢谢你，但问题是，如果我们在

ptr前设置一个双*，那么它读取对应于类型''double''的字节数。

我想要做的是决定字节数（

将来的类型）在''ptr''）前面的'switch-case''语句

一次，并在每次迭代中读取该字节数，将其转换为

双重型。例如，如果switch-case决定ptr将是
一个unsigned char *，那么而不是while循环中的double *，$
想要unsigned char *放在那里，然后将结果转换为

像这样：（double）（（unsigned char *）ptr）[k]。

这没有意义，如果ptr是unsigned char *，ptr [k + 1]将是一个

字节来自ptr [k]，所以它没有任何意义，并且可能会崩溃

诱导将这些任意字节序列转换为双倍。


-

Ian Collins。

Hi, i have a void pointer and i cast it to an appropriate known type
before using. The types which i cast this void* to are, from the
Intel''s open source computer vision library. Here is my piece of non-
working code:

CvMat *rowVect = cvCreateMat(1,nfeatures,CV_MAKETYPE(images[0]-

>depth,1));

//rowVect is a pointer to CvMat type

cvReshape( images[0], rowVect, 0, 1 ); //vectorize the image; readrow
is a 1xN matrix(vector)

void* ptr;

switch (images[0]->depth)
{
case IPL_DEPTH_8U :
ptr = (unsigned char *) rowVect->data.ptr ; //ptr is defined as an
unsigned char pointer
break; //
data is ''union'' type

case IPL_DEPTH_8S :
ptr = (signed char *) rowVect->data.ptr ;
break;

case IPL_DEPTH_16S :
ptr = (unsigned short *) rowVect->data.ptr ;
break;

case IPL_DEPTH_32S :
ptr = (int *) rowVect->data.i ; // i is defined as an int pointer
break;

case IPL_DEPTH _32F :
ptr = (float *) rowVect->data.fl ; // fl is defined as float
pointer
break;

case IPL_DEPTH_64F :
ptr = (double *) rowVect->data.db ; // db is a double
break;

}

int i=0, k;
while(i<nsamples)
{
cvReshape( images[i], readrow, 0, 1 );
for(k=0; k<nfeatures; k++)
Data->data.db[i*(Data->width)+k] = (double) ptr[k]; // errors occur
here
//fill the Data matrix
i++;
}

Error : 1) ''void*'' : unknown size
2) ''typecast'' : cannot convert from void to double

i m sorry if it is illegal to point a 3rd party library here, but it
has also been written in standard C. But my problem is a pure "C
language" problem i think. I cast a void pointer but then i cant use
it...

Regards

解决方案

On Sep 23, 7:14 pm, kkirtac <[e-mail]:

Hi, i have a void pointer and i cast it to an appropriate known type
before using. The types which i cast this void* to are, from the
Intel''s open source computer vision library. Here is my piece of non-
working code:

CvMat *rowVect = cvCreateMat(1,nfeatures,CV_MAKETYPE(images[0]->depth,1));

//rowVect is a pointer to CvMat type

cvReshape( images[0], rowVect, 0, 1 ); //vectorize the image; readrow
is a 1xN matrix(vector)

void* ptr;

switch (images[0]->depth)
{
case IPL_DEPTH_8U :
ptr = (unsigned char *) rowVect->data.ptr ; //ptr is defined as an
unsigned char pointer
break; //
data is ''union'' type

case IPL_DEPTH_8S :
ptr = (signed char *) rowVect->data.ptr ;
break;

case IPL_DEPTH_16S :
ptr = (unsigned short *) rowVect->data.ptr ;
break;

case IPL_DEPTH_32S :
ptr = (int *) rowVect->data.i ; // i is defined as an int pointer
break;

case IPL_DEPTH _32F :
ptr = (float *) rowVect->data.fl ; // fl is defined as float
pointer
break;

case IPL_DEPTH_64F :
ptr = (double *) rowVect->data.db ; // db is a double
break;

}

int i=0, k;
while(i<nsamples)
{
cvReshape( images[i], readrow, 0, 1 );
for(k=0; k<nfeatures; k++)
Data->data.db[i*(Data->width)+k] = (double) ptr[k]; // errors occur
here
//fill the Data matrix
i++;
}

Error : 1) ''void*'' : unknown size
2) ''typecast'' : cannot convert from void to double

i m sorry if it is illegal to point a 3rd party library here, but it
has also been written in standard C. But my problem is a pure "C
language" problem i think. I cast a void pointer but then i cant use
it...

Regards

Try rewriting (double) ptr[k] as ((double *)ptr)[k]

Regards,
B.

On Sep 23, 12:50 pm, [e-mail] wrote:

On Sep 23, 7:14 pm, kkirtac <[e-mail]:

Hi, i have a void pointer and i cast it to an appropriate known type
before using. The types which i cast this void* to are, from the
Intel''s open source computer vision library. Here is my piece of non-
working code:

CvMat *rowVect = cvCreateMat(1,nfeatures,CV_MAKETYPE(images[0]->depth,1));

//rowVect is a pointer to CvMat type

cvReshape( images[0], rowVect, 0, 1 ); //vectorize the image; readrow
is a 1xN matrix(vector)

void* ptr;

switch (images[0]->depth)
{
case IPL_DEPTH_8U :
ptr = (unsigned char *) rowVect->data.ptr ; //ptr is defined as an
unsigned char pointer
break; //
data is ''union'' type

case IPL_DEPTH_8S :
ptr = (signed char *) rowVect->data.ptr ;
break;

case IPL_DEPTH_16S :
ptr = (unsigned short *) rowVect->data.ptr ;
break;

case IPL_DEPTH_32S :
ptr = (int *) rowVect->data.i ; // i is defined as an int pointer
break;

case IPL_DEPTH _32F :
ptr = (float *) rowVect->data.fl ; // fl is defined as float
pointer
break;

case IPL_DEPTH_64F :
ptr = (double *) rowVect->data.db ; // db is a double
break;

}

int i=0, k;
while(i<nsamples)
{
cvReshape( images[i], readrow, 0, 1 );
for(k=0; k<nfeatures; k++)
Data->data.db[i*(Data->width)+k] = (double) ptr[k]; // errors occur
here
//fill the Data matrix
i++;
}

Error : 1) ''void*'' : unknown size
2) ''typecast'' : cannot convert from void to double

i m sorry if it is illegal to point a 3rd party library here, but it
has also been written in standard C. But my problem is a pure "C
language" problem i think. I cast a void pointer but then i cant use
it...

Regards

Try rewriting (double) ptr[k] as ((double *)ptr)[k]

Regards,
B.

Hmm thank you but the problem here is, if we set a double* in front of
ptr, then it reads amount of bytes that corresponds to type ''double''.
What i want to do here is to decide the amount of bytes(the type that
will come in front of ''ptr'') in the upper ''switch-case'' statement
once, and read that amount of bytes in each iteration, cast it to
double type. For instance, if the switch-case decides that ptr will be
an unsigned char* , then instead of the double* in the while loop, i
want unsigned char* be placed there, and then convert the result to
double like this : (double)((unsigned char *)ptr)[k] . But problem is
i want this to happen automatically..that i dont want to run the
switch-case inside the while loop to decide for that..I m sorry if it
got too complicated..
Regards

kkirtac wrote:

>
Hmm thank you but the problem here is, if we set a double* in front of
ptr, then it reads amount of bytes that corresponds to type ''double''.
What i want to do here is to decide the amount of bytes(the type that
will come in front of ''ptr'') in the upper ''switch-case'' statement
once, and read that amount of bytes in each iteration, cast it to
double type. For instance, if the switch-case decides that ptr will be
an unsigned char* , then instead of the double* in the while loop, i
want unsigned char* be placed there, and then convert the result to
double like this : (double)((unsigned char *)ptr)[k] .

That doesn''t make sense, if ptr is unsigned char*, ptr[k+1] will be one
byte on from ptr[k], so it makes no sense and is potentially crash
inducing to cast these arbitrary byte sequence to double.

--
Ian Collins.

这篇关于使用铸造空指针的问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！