C language implementation of string and memory library functions

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Preface

Their own string processing functions and memory processing functions . Contains only stdio.h file , Do not include third-party libraries .

About the function of each function , Please refer to the link below
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English links

One 、str

1.1 strlen

size_t MyStrlen(const char* str)
{
    
    size_t i = 0;
    while (str[i] != '\0')
    {
    
        i++;
    }
    return i;
}

1.2 strcmp

int MyStrcmp(const char* str1, const char* str2)
{
    
    char* String1 = (char*)str1;
    char* String2 = (char*)str2;

    for (; (*String1 == *String2); String2++)
    {
    
    	// if(*String1)
    	// String1++;
        if (!*String1++)
        {
    
            return (0);
        }
    }
    
    return ((unsigned char)*String1 - (unsigned char)*String2);
}

1.3 strstr

char* MyStrstr(const char* pszDst, const char* pszTag)
{
    
    char* pDest = (char*)pszDst;
    char* pRet = NULL;

    size_t i = 0;
    while (*pDest != '\0')
    {
    
        if (*pDest == *pszTag)
        {
    
            i = 0;
            while (pDest[i] == pszTag[i])
            {
    
                if (pszTag[i + 1] == '\0')
                {
    
                    pRet = pDest;
                    return pRet;
                }
                i++;
            }
        }

        pDest++;
    }

    return pRet;
}

1.4 strcpy

char* MyStrcpy(char* strDestination, const char* strSource)
{
    
    size_t i = 0;
    while (strSource[i] != '\0')
    {
    
        strDestination[i] = strSource[i];
        i++;
    }
    strDestination[i] = strSource[i];

    return strDestination;
}

1.5 strcat

char* MyStrcat(char* strDestination, const char* strSource)
{
    
    size_t i = 0;
    size_t j = 0;
    while (strDestination[i] != '\0')
    {
    
        i++;
    }

    while (strSource[j] != '\0')
    {
    
        strDestination[i] = strSource[j];
        j++;
        i++;
    }
    strDestination[i] = strSource[j];
    return strDestination;
}

Two 、mem

2.1 memset

void* MemorySet(void* pDest, int nValue, size_t nCount)
{
    
    while (nCount > 0)
    {
    
        ((char*)pDest)[nCount - 1] = nValue;
        nCount--;
    }
    return pDest;
}

2.2 memcpy

void* MemoryCopy(void* pDest, const void* pSrc, size_t nCount)
{
    
    char* pNew = (char*)pDest;
    char* pOld = (char*)pSrc;

    if (pNew < pOld)       //  From front to back 
    {
    
        while (nCount != 0)
        {
    
            *pNew = *pOld;
            pNew++;
            pOld++;
            nCount--;
        }
    }
    else                   //  From the back to the front 
    {
    
        pNew = pNew + nCount - 1;
        pOld = pOld + nCount - 1;
        while (nCount != 0)
        {
    
            *pNew = *pOld;
            pNew--;
            pOld--;
            nCount--;
        }
    }

    return pDest;
}

3、 ... and 、swap

void MySwap(int* const n1, int* const n2)
{
    
    int nTemp = *n1;
    *n1 = *n2;
    *n2 = nTemp;
}

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