根本字符串相关函数，基本宏，内存相关函数，类型转换函数实现合集

1．常用宏或函数的实现
_T，_L宏：
#define unsigned short L
#define _T(x)       __T(x)
#define _TEXT(x)    __T(x)

#ifdef  _UNICODE
#define __T(x) L##x     
#else
#define __T(x) x          
#endif

#define _L(x) L##x

assert宏实现：
#define assert(expr)
do{
    if (!(expr))
    {
            outputx("Assertion failed! %s, %s, %s, line %d\n",
                            #expr, __FILE__, __func__, __LINE__);
        }
}while(0)
assert函数实现：
inline bool Assert(bool result, const char* function, const char* file,  
                       int line, const char* expression)
{  
    if (!result)
    {  
            Log_Assert(function, file, line, expression);  
            Break();  
            return false;  
    }  
    return true;  
}

得到指定地址上的一个字节或字：
#define  MEM_B(x) (*((byte *)(x)))
#define  MEM_W(x) (*((word *)(x))  

得到一个变量的地址（word宽度）：
#define B_PTR(var)  ((byte *) (void *) &(var))
#define W_PTR(var)  ((word *) (void *) &(var))

得到一个字的高位和低位字节：
#define WORD_LO(xxx)  ((byte) ((word)(xxx) & 255))
#define WORD_HI(xxx)  ((byte) ((word)(xxx) >> 8))

将一个字母转换为大写：
#define UPCASE(c) (((c)>='a' && (c) <= 'z') ? ((c) - 0x20) : (c))

防止溢出的一个方法：
#define INC_SAT(val) (val=((val)+1>(val)) ? (val)+1 : (val))

DEBUG宏：
#ifdef _DEBUG
#define DEBUGMSG(msg,date) printf(msg);printf(“%d%d%d”,date,_LINE_,_FILE_)
#else
#define DEBUGMSG(msg,date)
#endif

2.字符串相关函数
int _strlen(const char* src)
{
    assert(src != NULL);
　　    const char *p = src;
　　    while(*p++!=NULL);
　　    return p - str - 1;
}

char* _strstr(const char* str, const char* sub)
{
    for(int i=0; str[i]!='\0'; i++)
    {
        int pos = i,j=0;
        while(str[i]==sub[j] && sub[j]!='\0')
        {
            ++i;
            ++j;
        }
        if(sub[j] == '\0')
            return &str[pos];
    }    

    return NULL;
}

char* _strncpy(char* dest, const char* src, int count)
{
    assert(dest!=NULL && src!=NULL && count>0);
    char* tmp = dest;
    while(count-->0 && (*dest++=*src++)!='\0');
    return tmp;
}

char* _strcpy(char* dest, const char* src)
{
    assert(dest!=NULL && src!=NULL);
    char* tmp = dest;
    while((*dest++=*src++) != '\0');
    return tmp;
}

int _strcmp(const char* first, const char* second)
{
    assert(first!=NULL && src!=second);
    int ret = 0;

    while(!(ret=(*(unsigned char*)first) - (*(unsigned char*)second))
        && (*first != '\0'))
    {
        ++first;
        ++second;
    }

    if(ret < 0)
        ret = -1;
    else if(ret > 0)
        ret = 1;
    
    return ret;
}

char* _strcat(char* dest,char* src)
{
    assert(dest!=NULL && src!=NULL);
    char* tmp = dest;

    while(*dest != '\0')
        ++dest;
    while(((*dest++)=(*src++)) != '\0');
    return tmp;
}

void _loopmove(char* str, int steps)
{
    int n = strlen(str)-steps;
    char tmp[256];
    memcpy(tmp,str+n,steps);
    memcpy(str+steps,str,n);
    memcpy(str,tmp,steps);
}

char* _reversestring(char* src)
{
    assert(src!=NULL);
    int len=strlen(src);
    char tmp = '\0';
    
    for(int i=0; i<len/2; i++)
    {
        tmp = src[i];
        src[i] = src[len-i-1];
        src[len-i-1] = tmp;
    }
    return src;
}

void _makepath(char* path, const char* drive, const char* dir, const char*filename, const char* ext)
{
    assert(path!=NULL && drive!=NULL && filename!=NULL && ext!=NULL);

    register const char* p;
    if(*drive)
    {
        *path++ = *drive;
        *path++ = ':';
        *path++ = '\\';
    }
    else
        return;

    if((p=dir) && *p)
    {
        do
        {
            *path++ = *p++;
        }while(*p);
        if(*(p-1) != '\\')
            *path++ = '\\';
    }
    
    if(p = filename)
    {
        while(*p)
            *path++ = *p++;
    }

    if(p = ext)
    {
        if(*p && *p != '.')
            *path++ = '.';
        while(*path++ = *p++);
    }

    *path++ = '\0';
}

3.内存相关函数
void* _memset(void* dest, int c,int count)
{
    assert(dest != NULL);
    char* tmp = (char*)dest;
    int i = 0;
    
    while(count--)
        dest[i++] = c;

    return tmp;
}

void _memcpy(void* dest, const void* src, int count)
{
    assert(dest!=NULL && src!=NULL);
    unsigned char* pdst = (unsigned char*)dest;
    unsigned char* psrc = (unsigned char*)src;
    assert(!(psrc<=pdst && pdst<psrc+count));
    assert(!(pdst<=psrc && psrc<pdst+count));

    while(count--)
        *pdst++ = *psrc++;     
}

4.类型转换函数
void _itoa(long num,char str[],int radix)  
{  
    if( str == NULL)
        return;
    long sign = num,i = 0,j = 0;  
        char temp[100];  
 
        if(sign < 0)  
            num = -num;  
   
        do  
        {  
            temp[i] = num % radix+'0';  
            num /= radix;  
            i++;  
        }while(num > 0);  
    
    if(sign < 0)  
            temp[i++] = '-';    
        temp[i] = '\0';  
        i--;   
 
        while(i >= 0)  
        {  
            str[j] = temp[i];  
            j++;  
            i--;  
        }  
        str[j] = '\0';  
}

void _ftoa(float number,int ndigit,char buf[])
{
    assert(buf!=NULL);
    
    long int_part;  
        double float_part;  
        char str_int[512];  
        char str_float[256];  
        memset(str_int,0,512);  
        memset(str_float,0,256);  
        int_part = (long)number;  
        float_part = number - int_part;  
        _itoa(int_part,str_int,10);  
 
       if(ndigit>0)  
        {  
            float_part =fabs(pow(10,ndigit)*float_part);  
            _itoa((long)float_part,str_float,10);  
        }  
        int i = strlen(str_int);  
        str_int[i] = '.';  
        strcat(str_int,str_float);  
        strcpy(buf,str_int);  
}

int _atoi(const char str[])  
{  
        int ret_Integer = 0;  
        int integer_Sign = 1;  
      
        if(str == NULL)  
            return 0;   

        while(*str == ' ')  
            str++;  

        if(*str == '-')  
            integer_Sign = -1;  
    
        if(*str == '-' || *str == '+')  
            str++;   

        while(*str >= '0' && *str <= '9')  
        {  
            ret_Integer = ret_Integer * 10 + *str - '0';  
            str++;  
        }  
        ret_Integer = integer_Sign * ret_Integer;  
      
        return ret_Integer;  
}

float _atof(const char str[])  
{  
    if(str == NULL)  
            return 0.0;
 
        int len = strlen(str),i = 0;  
        if(str[0] == '-')  
        i++;  
      
        float s = 0.0;  
        while(i < len && (str[i]>='0' && str[i]<='9'))  
        {  
            s = s * 10 + (float)(str[i]-'0');  
            i++;  
        }  
          
        if(str[i] == '.')
        i++;  
        else
        return s;  
      
        float order = 1.0;  
        while(i < len && (str[i]>='0' && str[i]<='9'))  
        {  
            order = order / 10;  
            s = s + (float)(str[i]-'0')*order;  
            i++;  
        }  
      
        if (str[i] == '-')
        s = -1*s;  
      
        return s;  
    }   


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