C/C ++ HDF5读取字符串属性 [英] C/C++ HDF5 Read string attribute
问题描述
我的一位同事使用labview将ASCII字符串作为属性写入HDF5文件中.我可以看到该属性存在,并且可以读取,但是无法打印.
A colleague of mine used labview to write an ASCII string as an attribute in an HDF5 file. I can see that the attribute exist, and read it, but I can't print it.
该属性是,如HDF Viewer中所示:
The attribute is, as shown in HDF Viewer:
日期= 2015 \ 07 \ 09
Date = 2015\07\09
所以日期"是它的名字.
So "Date" is its name.
我正在尝试使用此代码读取属性
I'm trying to read the attribute with this code
hsize_t sz = H5Aget_storage_size(dateAttribHandler);
std::cout<<sz<<std::endl; //prints 16
hid_t atype = H5Aget_type(dateAttribHandler);
std::cout<<atype<<std::endl; //prints 50331867
std::cout<<H5Aread(dateAttribHandler,atype,(void*)date)<<std::endl; //prints 0
std::cout<<date<<std::endl; //prints messy characters!
//even with an std::string
std::string s(date);
std::cout<<s<<std::endl; //also prints a mess
为什么会这样?我如何以const char*
或std::string
的形式获取此字符串?
Why is this happening? How can I get this string as a const char*
or std::string
?
我也尝试过使用类型atype = H5Tcopy (H5T_C_S1);
,但这也不起作用...
I tried also using the type atype = H5Tcopy (H5T_C_S1);
, and that didn't work too...
在这里,我根据要求提供了一个完整的,自包含的程序:
Here I provide a full, self-contained program as it was requested:
#include <string>
#include <iostream>
#include <fstream>
#include <hdf5/serial/hdf5.h>
#include <hdf5/serial/hdf5_hl.h>
std::size_t GetFileSize(const std::string &filename)
{
std::ifstream file(filename.c_str(), std::ios::binary | std::ios::ate);
return file.tellg();
}
int ReadBinFileToString(const std::string &filename, std::string &data)
{
std::fstream fileObject(filename.c_str(),std::ios::in | std::ios::binary);
if(!fileObject.good())
{
return 1;
}
size_t filesize = GetFileSize(filename);
data.resize(filesize);
fileObject.read(&data.front(),filesize);
fileObject.close();
return 0;
}
int main(int argc, char *argv[])
{
std::string filename("../Example.hdf5");
std::string fileData;
std::cout<<"Success read file into memory: "<<
ReadBinFileToString(filename.c_str(),fileData)<<std::endl;
hid_t handle;
hid_t magFieldsDSHandle;
hid_t dateAttribHandler;
htri_t dateAtribExists;
handle = H5LTopen_file_image((void*)fileData.c_str(),fileData.size(),H5LT_FILE_IMAGE_DONT_COPY | H5LT_FILE_IMAGE_DONT_RELEASE);
magFieldsDSHandle = H5Dopen(handle,"MagneticFields",H5P_DEFAULT);
dateAtribExists = H5Aexists(magFieldsDSHandle,"Date");
if(dateAtribExists)
{
dateAttribHandler = H5Aopen(magFieldsDSHandle,"Date",H5P_DEFAULT);
}
std::cout<<"Reading file done."<<std::endl;
std::cout<<"Open handler: "<<handle<<std::endl;
std::cout<<"DS handler: "<<magFieldsDSHandle<<std::endl;
std::cout<<"Attributes exists: "<<dateAtribExists<<std::endl;
hsize_t sz = H5Aget_storage_size(dateAttribHandler);
std::cout<<sz<<std::endl;
char* date = new char[sz+1];
std::cout<<"mem bef: "<<date<<std::endl;
hid_t atype = H5Aget_type(dateAttribHandler);
std::cout<<atype<<std::endl;
std::cout<<H5Aread(dateAttribHandler,atype,(void*)date)<<std::endl;
fprintf(stderr, "Attribute string read was '%s'\n", date);
date[sz] = '\0';
std::string s(date);
std::cout<<"mem aft: "<<date<<std::endl;
std::cout<<s<<std::endl;
H5Dclose(magFieldsDSHandle);
H5Fclose(handle);
return 0;
}
该程序的打印输出:
Success read file into memory: 0
Reading file done.
Open handler: 16777216
DS handler: 83886080
Attributes exists: 1
16
mem bef:
50331867
0
Attribute string read was '�P7'
mem aft: �P7
�P7
Press <RETURN> to close this window...
谢谢.
推荐答案
原来,必须使用char指针的引用来调用H5Aread
……所以指针的指针:
It turned out that H5Aread
has to be called with a reference of the char pointer... so pointer of a pointer:
H5Aread(dateAttribHandler,atype,&date);
请记住,不必为此保留内存.该库将保留内存,然后您可以使用H5free_memory(date)
释放它.
Keep in mind that one doesn't have to reserve memory for that. The library will reserve memory, and then you can free it with H5free_memory(date)
.
这很好.
我了解到只有当要读取的字符串具有可变长度时才是这种情况.如果字符串的长度固定,则必须手动保留大小为length+1
的内存,甚至手动将最后一个字符设置为null(以获取以null结尾的字符串.hdf5库中有一个函数可以检查是否字符串的长度是固定的.
I learned that this is the case only when the string to be read has variable length. If the string has a fixed length, then one has to manually reserve memory with size length+1
and even manually set the last char to null (to get a null-terminated string. There is a function in the hdf5 library that checks whether a string is fixed in length.
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