When you’re at a Unix terminal and your terminal goes screwy, try typing “stty sane” to reset it. Handy!
stty sane
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Daily Archives: 2012-01-04 [Wednesday]
printf thousands separator
It took me a while, but I finally found this documentation which said that you use the single quote to flag formatted output as having the thousands separator when using printf.
MD5 in C++
MD5 in C++ is everywhere if you search for it (except for in the standard library or in boost, which isn’t what I would have expected), but I only needed one implementation and I found this one: RSA Data Security, Inc. MD5 Message-Digest Algorithm.
Detecting if code is compiling under Visual Studio
I wanted to figure out how to tell if my code was compiling in Visual Studio or somewhere else (GCC probably), and I found that you can use #ifdef _MSC_VER.
Enabling Windows SDK 7.1 in Visual Studio 2008
I was having a problem where Visual Studio was saying that “windows.h” could not be found after having installed the Windows SDK v7.1. I found this article which said to update the path in “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SDKs\Windows\CurrentInstallFolder” in the registry. So I did that, and now everything is working.
Operator overloading in C++
I did my first operator overloading in C++ today. My code ended up being quite different to the example code that I found, but I think I’m happy with it:
class FileData {
public:
FileData( const string& path );
static bool LessThan( const FileData& a, const FileData& b );
bool operator< ( const FileData& );
unsigned long size() const { return m_size; }
private:
unsigned long m_size;
char m_md5[ 16 ];
};
static bool operator< ( const FileData& a, const FileData& b ) {
return FileData::LessThan( a, b );
}
bool FileData::operator< ( const FileData& b ) {
return FileData::LessThan( *this, b );
}
bool FileData::LessThan ( const FileData& a, const FileData& b ) {
unsigned long a_size = a.size();
unsigned long b_size = b.size();
if ( a_size == b_size ) {
return memcmp( a.m_md5, b.m_md5, 16 ) < 0;
}
return a_size < b_size;
}
I'm not sure when it becomes either useful or necessary to define the operator both as a static and as a member function. I did both because I wasn't sure what was required.
Differences between C++ pointers and C++ references
I was curious about the difference between C++ pointers and C++ references, so I searched and found this which says that basically:
- It’s not necessary to initialise pointers at declaration time, but it is necessary to initialise references at declaration time.
- You can create an array of pointers, but you can’t create an array of references.
- You can assign null to pointers, but you can’t assign null to references.
Reading binary files in C++
I learned how to read binary files in C++ today. My function (which creates an MD5 hash of a file) ended up looking a little different to the example that I learned from:
const int BUFFER_SIZE = 1024;
int length;
char buffer[ BUFFER_SIZE ];
MD5_CTX ctx;
MD5Init( &ctx );
ifstream is( path.c_str(), ios::binary );
while ( is.good() ) {
is.read( (char *)buffer, BUFFER_SIZE );
streamsize count = is.gcount();
MD5Update( &ctx, (unsigned char *)buffer, count );
}
if ( is.eof() ) {
// it's ok, we're at the end of the file
}
else if ( is.bad() ) {
// bad bit is set
cout << "Bad bit is set while reading '" << path << "'." << endl;
cout << strerror( errno ) << endl;
exit ( 1 );
}
else if ( is.fail() ) {
cout << "Fail bit is set while reading '" << path << "'." << endl;
cout << strerror( errno ) << endl;
exit( 1 );
}
is.close();
Fatal error LNK1120: unresolved externals, caused by C functions in C++
I was receiving link error LNK1120 in Visual Studio after adding some C code to my C++ project, and the problem was, as I discovered here (and found more info on here), that I hadn’t declared my C code as “extern C”.
So basically I added #ifdef __cplusplus macros to check if it was C or C++ code and if C++ then outputting “extern C {” with a suitable “}” at the end of the file.
Don’t use memcmp to compare structs or classes
Structs and classes can be laid out with padding between the data members for alignment purposes, and this padding doesn’t get initialised unless you specifically zero it out yourself. So if you’re using memcmp and comparing memory at pointers to structs you might have a problem if you’re expecting structs with equal data members to always be equal.