C++问题点摘录（持续更新）

来源：互联网发布：centos安装armlinuxgcc 编辑：程序博客网时间：2024/06/05 07:07

1.一般如果有比较大小的时候。使用unsigned来比较，这个和默认的比较结果相同。

2.定义bool类型的值时。默认的值时ture的。

3.如果有无用的函数参数，可以采用宏命令无视掉。UNREFERENCED_PARAMETER（）

4._strlwr(buf);使用_strlwr_s(buf, sizeof(buf));替换

5.sscanf( tokenstring, "%c", &c );用sscanf_s( tokenstring, "%c", &c, sizeof(char) );替换

6.UINT WINAPI GetTempFileName(
__in   LPCTSTR lpPathName,//路径
__in   LPCTSTR lpPrefixString, //临时文件名的头部
__in   UINT uUnique,//0就可以了，有很多好处

__out LPTSTR lpTempFileName
);

创建磁盘上唯一命名的零字节的临时文件并返回该文件的完整路径。创建带 .TMP 文件扩展名

如果使用 GetTempFileName 方法创建超过 65535 个文件但不删除以前的临时文件，则将引发IOException。

如果没有提供唯一的临时文件名，则GetTempFileName 方法将引发IOException。要解决此错误，请删除所有不需要的临时文件。

失败返回0.

7.DWORD WINAPI GetTempPath(
__in DWORD nBufferLength,
__out LPTSTR lpBuffer
);获取临时文件夹。返回字符串长度。包含“/”符号

void GetMyDocumentFolder(CString &m_Folder)
{
LPITEMIDLIST pidl ;
TCHAR szInitialFolder[MAX_PATH] ;

_tcscpy_s(szInitialFolder, ARRAYSIZE(szInitialFolder), _T(".")) ; // cold position (this may locate install folder)

m_Folder = _T(".") ;

IMalloc *pMalloc;
if ( SUCCEEDED(SHGetMalloc(&pMalloc)) )
{
  if( SUCCEEDED(SHGetSpecialFolderLocation(NULL, CSIDL_PERSONAL, &pidl)) )
  {
   SHGetPathFromIDList(pidl,szInitialFolder);
   pMalloc->Free(pidl);
  }
  pMalloc->Release();
  m_Folder = (LPCTSTR)szInitialFolder ;
}
}

获取临时文件夹路径

更新版：

void GetTempFile(
   CString strFix,     // <IN> Top of 2 characters to be make file name
   CString &strTempFileName  // <OUT> File name (full path)
  )
{
BOOL bSuccess = FALSE ;
TCHAR szTempPath[MAX_PATH] ;
TCHAR szTempFileName[MAX_PATH] ;
int  nTempLen ;
nTempLen = ::GetTempPath( sizeof(szTempPath)/sizeof(TCHAR), szTempPath ) ;

strFix.Left(2) ;
if ( (0 < nTempLen) && (nTempLen < MAX_PATH) )
{
  if ( 0 != ::GetTempFileName(szTempPath, strFix, 0, szTempFileName) )
  {
   bSuccess = TRUE ;
  }
}
if ( !bSuccess )
{
  CString  m_Folder ;
  BRUtility::GetMyDocumentFolder(m_Folder) ;
  GetTempFileName((LPCTSTR)m_Folder, strFix, 0, szTempFileName) ;
}
strTempFileName = (CString)szTempFileName ;
}

8.16进制与10进制互换

int hex2num(char hex) {
int result = -1;
unsigned work = (unsigned)hex;
if(work >= '0' && work <= '9') {
  result = work - '0';
}
else if(work >= 'a' && work <= 'f') {
  result = 10 + work - 'a';
}
else if(work >= 'A' && work <= 'F') {
  result = 10 + work - 'A';
}
return result;
}

char num2hex(int num) {
char result = -1;
unsigned work = (unsigned)num;
if(work >= 0 && work <= 9) {
result = work + '0';
}
else if(work >= 0x0A && work <= 0x0F) {
result = (work - 10) + 'A';
}
return result;
}
//0123456789ABCDEF"→0x01, 0x23,0x45,0x67,0x89,0xAB,0xCD,0xEF

bool str2hex(char* src, char* dst) {
bool result = true;
size_t len = strlen(src)/2;
char *buff = (char*)alloca(len);
for(unsigned i=0 ; i<::strlen(src) ; i += 2) {
  int h = hex2num(src[i]);
  int l = hex2num(src[i+1]);
  if(h < 0 || l < 0) {
   result = false;
   break;
  }
  buff[i/2] = (h<<4) + l;
}
if(result)
  memcpy(dst, buff, len);

return result;
}

//0x01, 0x23,0x45,0x67,0x89,0xAB,0xCD,0xEF→"0123456789ABCDEF"

bool hex2str(char* src, char* dst, unsigned len) {
bool result = true;
char *buff = (char*)alloca(len * 2);
for(unsigned i=0 ; i<len ; i++) {
  int h = num2hex((src[i] & 0xF0) >> 4);
  int l = num2hex(src[i] & 0x0F);
  if(h < 0 || l < 0) {
   result = false;
   break;
  }
  buff[i*2] = h;
  buff[i*2 + 1] = l;
}
if(result)
  memcpy(dst, buff, len * 2);

return result;
}

9.判断版本

int DecideOSVersion()

{
OSVERSIONINFO info;

info.dwOSVersionInfoSize = sizeof(info);
if( GetVersionEx(&info) ) {
if( 6 <= info.dwMajorVersion ){ // Vista or later
}
}
return info.dwMajorVersion ;
}

新版本

  OSVERSIONINFOEX sVerInfo;
  DWORDLONG dwlConditionMask = 0;
  sVerInfo.dwOSVersionInfoSize = sizeof( OSVERSIONINFO );

  // Initialize the OSVERSIONINFOEX structure.
  ZeroMemory(&sVerInfo, sizeof(OSVERSIONINFOEX));
  sVerInfo.dwOSVersionInfoSize = sizeof(OSVERSIONINFOEX);
  sVerInfo.dwMajorVersion = 5; // XP
  sVerInfo.dwMinorVersion = 1; // XP
  //sVerInfo.wServicePackMajor = 0;

  // Initialize the condition mask.
  VER_SET_CONDITION( dwlConditionMask, VER_MAJORVERSION, VER_GREATER_EQUAL );
  VER_SET_CONDITION( dwlConditionMask, VER_MINORVERSION, VER_GREATER_EQUAL );
  VER_SET_CONDITION( dwlConditionMask, VER_SERVICEPACKMAJOR, VER_GREATER_EQUAL );

  if (VerifyVersionInfo(&sVerInfo, VER_MAJORVERSION
     | VER_MINORVERSION
     | VER_SERVICEPACKMAJOR,
     dwlConditionMask) != FALSE)  {

Xp以后

}else{

Xp之前

}

10.strtok使用

  char *cp = NULL;
  char *next_token = NULL;
  cp = strtok_s(FilterData2->IpAddressList, "\n", &next_token);
  while ( cp != NULL)
  {
   FilterData.IpAddressList.push_back(cp) ;
   cp = strtok_s(NULL, "\n", &next_token) ;
  }

11.默认debug时候的字符串填充是fe，（MSDN上有描述，为了更好的找到错误）如果要忽略这个技能，

可以设置成自己想要的填充符，如果要填充0，定义下面的宏

_CrtSetDebugFillThreshold( 0 );

12.时间函数的理解（个人，非官方）

time_t time( time_t *timer );获取当前系统时间，跟时区有关。

struct tm *gmtime( const time_t *timer );获取time_t的时间到tm类型。会根据系统减去多余的时区时间恢复到UTC时间。

time_t mktime( struct tm *timeptr );把当地时间以格式化输出。

13Mutex运用（CreateMutex权限不够会返回NULL）

int GetMutexObject( HANDLE* h_mutex, char * MutexName, bool * isAlreadyExist )
{
int status = 0;

(*isAlreadyExist) = false;

// Make Mutex-Name
char mutex_name[MAX_PATH];
OSVERSIONINFO OsVersionInfo;
OsVersionInfo.dwOSVersionInfoSize = sizeof(OsVersionInfo);

GetVersionEx(&OsVersionInfo);

// Windows 2000 or later
if( 5 <= OsVersionInfo.dwMajorVersion )
{
  strcpy_s(mutex_name, sizeof(mutex_name), "Global\\");
  strncat_s(mutex_name, sizeof(mutex_name), MutexName, _TRUNCATE);
}
else
{
  strcpy_s(mutex_name, sizeof(mutex_name), MutexName);
}

*h_mutex = CreateMutex(
          NULL,
          FALSE,
          mutex_name
           );

DWORD err = ::GetLastError();
if(( err == ERROR_ALREADY_EXISTS )||( err == ERROR_ACCESS_DENIED))
{
  if(NULL != *h_mutex)
  {
   CloseHandle(*h_mutex);
  }
  (*isAlreadyExist) = true;
}

return status;
}

void ReleaseMutexObject( HANDLE* h_mutex )
{

ReleaseMutex(*h_mutex);
CloseHandle(*h_mutex);
}

外部使用范例

HANDLE hd2;
bool bFlag = FALSE;
GetMutexObject(&hd2, MUTEX_ALL, &bFlag);
if(!bFlag){
ReleaseMutexObject(&hd2);
}