sizeof与strlen的区别

char str[10]="12345";

例如给出一个字符串数组，做如下运算（假设在32位架构处理器下）：

int a = sizeof(str);/*a=10,sizeof计算的是字符串数组str[10]所占的内存空间大小，仅与数组的类型有关，与数组内存储内容无关，此处char在32位架构下占用内存空间为1个字节*/

int b = strlen(str);/* b=5,strlen计算的是数组内字符串的长度，以\0'为字符串结束标记，计算长度不包含\0*/

通常在利用malloc进行内存空间分配的时候，会使用sizeof来计算结构体指针所需的内存空间大小，以此来分配空间。  

e.g.

/* The definition of the timers themselves. */
typedef struct tmrTimerControl
{
const char *pcTimerName; /*<< Text name.  This is not used by the kernel, it is included simply to make debugging easier. */ /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
ListItem_t xTimerListItem; /*<< Standard linked list item as used by all kernel features for event management. */
TickType_t xTimerPeriodInTicks;/*<< How quickly and often the timer expires. */
UBaseType_t uxAutoReload; /*<< Set to pdTRUE if the timer should be automatically restarted once expired.  Set to pdFALSE if the timer is, in effect, a one-shot timer. */
void *pvTimerID; /*<< An ID to identify the timer.  This allows the timer to be identified when the same callback is used for multiple timers. */
TimerCallbackFunction_t pxCallbackFunction; /*<< The function that will be called when the timer expires. */
#if( configUSE_TRACE_FACILITY == 1 )
UBaseType_t uxTimerNumber; /*<< An ID assigned by trace tools such as FreeRTOS+Trace */
#endif


#if( ( configSUPPORT_STATIC_ALLOCATION == 1 ) && ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) )
uint8_t ucStaticallyAllocated; /*<< Set to pdTRUE if the timer was created statically so no attempt is made to free the memory again if the timer is later deleted. */
#endif
} xTIMER;


/* The old xTIMER name is maintained above then typedefed to the new Timer_t
name below to enable the use of older kernel aware debuggers. */
typedef xTIMER Timer_t;

使用示例：pxNewTimer = ( Timer_t * ) pvPortMalloc( sizeof( Timer_t ) );

或者清空结构体内的变量时使用sizeof计算所占用的内存空间。

e.g.

/**
 * Summary GPS information from all parsed packets,
 * used also for generating NMEA stream
 * @see nmea_parse
 * @see nmea_GPGGA2info,  nmea_...2info
 */
typedef struct _nmeaINFO
{
    int     smask;      /**< Mask specifying types of packages from which data have been obtained */


    nmeaTIME utc;       /**< UTC of position */


    int     sig;        /**< GPS quality indicator (0 = Invalid; 1 = Fix; 2 = Differential, 3 = Sensitive) */
    int     fix;        /**< Operating mode, used for navigation (1 = Fix not available; 2 = 2D; 3 = 3D) */


    double  PDOP;       /**< Position Dilution Of Precision */
    double  HDOP;       /**< Horizontal Dilution Of Precision */
    double  VDOP;       /**< Vertical Dilution Of Precision */


    double  lat;        /**< Latitude in NDEG - +/-[degree][min].[sec/60] */
    double  lon;        /**< Longitude in NDEG - +/-[degree][min].[sec/60] */
    double  elv;        /**< Antenna altitude above/below mean sea level (geoid) in meters */
    double  speed;      /**< Speed over the ground in kilometers/hour */
    double  direction;  /**< Track angle in degrees True */
    double  declination; /**< Magnetic variation degrees (Easterly var. subtracts from true course) */


    nmeaSATINFO satinfo; /**< Satellites information */


} nmeaINFO;

使用示例： memset(info, 0, sizeof(nmeaINFO));