常见的C字符串处理函数的源代码

char *strcpy(char *strDes, const char *strSrc)

{

assert((strDes != NULL) && (strSrc != NULL));

char *address = strDes;

while ((*strDes ++ = *strSrc ++) != '/0')

NULL;

return address;

}

char *strchr_(char *str, int c)

{

assert(str != NULL);

while ((*str != (char) c) && (*str != '/0'))

str ++;

if (*str != '/0')

return str;

return NULL;

}

char *strchr(const char *str, int c)

{

assert(str != NULL);

for (; *str != (char) c; ++ str)

if (*str == '/0')

return NULL;

return (char *) str;

}

int strcmp(const char *s, const char *t)

{

assert(s != NULL && t != NULL);

while (*s && *t && *s == *t)

{

++ s;

++ t;

}

return (*s - *t);

}

char *strcat(char *strDes, const char *strSrc)

{

assert((strDes != NULL) && (strSrc != NULL));

char *address = strDes;

while (*strDes != '/0')

++ strDes;

while ((*strDes ++ = *strSrc ++) != '/0')

NULL;

return address;

}

int strlen(const char *str)

{

assert(str != NULL);

int len = 0;

while (*str ++ != '/0')

++ len;

return len;

}

char *strdup(const char *strSrc)

{

assert(strSrc != NULL);

int len = 0;

while (*strSrc ++ != '/0')

++ len;

char *strDes = (char *) malloc (len + 1);

while ((*strDes ++ = *strSrc ++) != '/0')

NULL;

return strDes;

}

char *strstr(const char *strSrc, const char *str)

{

assert(strSrc != NULL && str != NULL);

const char *s = strSrc;

const char *t = str;

for (; *t != '/0'; ++ strSrc)

{

for (s = strSrc, t = str; *t != '/0' && *s == *t; ++s, ++t)

NULL;

if (*t == '/0')

return (char *) strSrc;

}

return NULL;

}

char *strncpy(char *strDes, const char *strSrc, int count)

{

assert(strDes != NULL && strSrc != NULL);

char *address = strDes;

while (count -- && *strSrc != '/0')

*strDes ++ = *strSrc ++;

return address;

}

char *strncat(char *strDes, const char *strSrc, int count)

{

assert((strDes != NULL) && (strSrc != NULL));

char *address = strDes;

while (*strDes != '/0')

++ strDes;

while (count -- && *strSrc != '/0' )

*strDes ++ = *strSrc ++;

*strDes = '/0';

return address;

}

int strncmp(const char *s, const char *t, int count)

{

assert((s != NULL) && (t != NULL));

while (*s && *t && *s == *t && count --)

{

++ s;

++ t;

}

return (*s - *t);

}

char *strpbrk(const char *strSrc, const char *str)

{

assert((strSrc != NULL) && (str != NULL));

const char *s;

while (*strSrc != '/0')

{

s = str;

while (*s != '/0')

{

if (*strSrc == *s)

return (char *) strSrc;

++ s;

}

++ strSrc;

}

return NULL;

}

int strcspn(const char *strSrc, const char *str)

{

assert((strSrc != NULL) && (str != NULL));

const char *s;

const char *t = strSrc;

while (*t != '/0')

{

s = str;

while (*s != '/0')

{

if (*t == *s)

return t - strSrc;

++ s;

}

++ t;

}

return 0;

}

int strspn(const char *strSrc, const char *str)

{

assert((strSrc != NULL) && (str != NULL));

const char *s;

const char *t = strSrc;

while (*t != '/0')

{

s = str;

while (*s != '/0')

{

if (*t == *s)

break;

++ s;

}

if (*s == '/0')

return t - strSrc;

++ t;

}

return 0;

}

char *strrchr(const char *str, int c)

{

assert(str != NULL);

const char *s = str;

while (*s != '/0')

++ s;

for (-- s; *s != (char) c; -- s)

if (s == str)

return NULL;

return (char *) s;

}

char* strrev(char *str)

{

assert(str != NULL);

char *s = str, *t = str, c;

while (*t != '/0')

++ t;

for (-- t; s < t; ++ s, -- t)

{

c = *s;

*s = *t;

*t = c;

}

return str;

}

char *strnset(char *str, int c, int count)

{

assert(str != NULL);

char *s = str;

for (; *s != '/0' && s - str < count; ++ s)

*s = (char) c;

return str;

}

char *strset(char *str, int c)

{

assert(str != NULL);

char *s = str;

for (; *s != '/0'; ++ s)

*s = (char) c;

return str;

}

char *strtok(char *strToken, const char *str)

{

assert(strToken != NULL && str != NULL);

char *s = strToken;

const char *t = str;

while (*s != '/0')

{

t = str;

while (*t != '/0')

{

if (*s == *t)

{

*(strToken + (s - strToken)) = '/0';

return strToken;

}

++ t;

}

++ s;

}

return NULL;

}

char *strupr(char *str)

{

assert(str != NULL);

char *s = str;

while (*s != '/0')

{

if (*s >= 'a' && *s <= 'z')

*s -= 0x20;

s ++;

}

return str;

}

char *strlwr(char *str)

{

assert(str != NULL);

char *s = str;

while (*s != '/0')

{

if (*s >= 'A' && *s <= 'Z')

*s += 0x20;

s ++;

}

return str;

}

void *memcpy(void *dest, const void *src, int count)

{

assert((dest != NULL) && (src != NULL));

void *address = dest;

while (count --)

{

*(char *) dest = *(char *) src;

dest = (char *) dest + 1;

src = (char *) src + 1;

}

return address;

}

void *memccpy(void *dest, const void *src, int c, unsigned int count)

{

assert((dest != NULL) && (src != NULL));

while (count --)

{

*(char *) dest = *(char *) src;

if (* (char *) src == (char) c)

return ((char *)dest + 1);

dest = (char *) dest + 1;

src = (char *) src + 1;

}

return NULL;

}

void *memchr(const void *buf, int c, int count)

{

assert(buf != NULL);

while (count --)

{

if (*(char *) buf == c)

return (void *) buf;

buf = (char *) buf + 1;

}

return NULL;

}

int memcmp(const void *s, const void *t, int count)

{

assert((s != NULL) && (t != NULL));

while (*(char *) s && *(char *) t && *(char *) s == *(char *) t && count --)

{

s = (char *) s + 1;

t = (char *) t + 1;

}

return (*(char *) s - *(char *) t);

}

void *memmove(void *dest, const void *src, int count)

{

assert(dest != NULL && src != NULL);

void *address = dest;

while (count --)

{

*(char *) dest = *(char *) src;

dest = (char *) dest + 1;

src = (const char *)src + 1;

}

return address;

}

void *memset(void *str, int c, int count)

{

assert(str != NULL);

void *s = str;

while (count --)

{

*(char *) s = (char) c;

s = (char *) s + 1;

}

return str;

}