C++字符串函数

函数名: stpcpy
功 能: 拷贝一个字符串到另一个
用 法: char *stpcpy(char *destin, char *source);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char string[10];
char *str1 = "abcdefghi";

stpcpy(string, str1);
printf("%s/n", string);
return 0;
}

函数名: strcat
功 能: 字符串拼接函数
用 法: char *strcat(char *destin, char *source);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char destination[25];
char *blank = " ", *c = "C++", *Borland = "Borland";

strcpy(destination, Borland);
strcat(destination, blank);
strcat(destination, c);

printf("%s/n", destination);
return 0;
}

函数名: strchr
功 能: 在一个串中查找给定字符的第一个匹配之处/
用 法: char *strchr(char *str, char c);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char string[15];
char *ptr, c = 'r';

strcpy(string, "This is a string");
ptr = strchr(string, c);
if (ptr)
printf("The character %c is at position: %d/n", c, ptr-string);
else
printf("The character was not found/n");
return 0;
}

函数名: strcmp
功 能: 串比较
用 法: int strcmp(char *str1, char *str2);
看Asic码，str1>str2，返回值 > 0；两串相等，返回0
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *buf1 = "aaa", *buf2 = "bbb", *buf3 = "ccc";
int ptr;

ptr = strcmp(buf2, buf1);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");
else
printf("buffer 2 is less than buffer 1/n");

ptr = strcmp(buf2, buf3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 3/n");
else
printf("buffer 2 is less than buffer 3/n");

return 0;
}

函数名: strncmpi
功 能: 将一个串中的一部分与另一个串比较, 不管大小写
用 法: int strncmpi(char *str1, char *str2, unsigned maxlen);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *buf1 = "BBB", *buf2 = "bbb";
int ptr;

ptr = strcmpi(buf2, buf1);

if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");

if (ptr < 0)
printf("buffer 2 is less than buffer 1/n");

if (ptr == 0)
printf("buffer 2 equals buffer 1/n");

return 0;
}

函数名: strcpy
功 能: 串拷贝
用 法: char *strcpy(char *str1, char *str2);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char string[10];
char *str1 = "abcdefghi";

strcpy(string, str1);
printf("%s/n", string);
return 0;
}

函数名: strcspn
功 能: 在串中查找第一个给定字符集内容的段
用 法: int strcspn(char *str1, char *str2);
程序例:

#include <stdio.h>
#include <string.h>
#include <alloc.h>

int main(void)
{
char *string1 = "1234567890";
char *string2 = "747DC8";
int length;

length = strcspn(string1, string2);
printf("Character where strings intersect is at position %d/n", length);

return 0;
}

函数名: strdup
功 能: 将串拷贝到新建的位置处
用 法: char *strdup(char *str);
程序例:

#include <stdio.h>
#include <string.h>
#include <alloc.h>

int main(void)
{
char *dup_str, *string = "abcde";

dup_str = strdup(string);
printf("%s/n", dup_str);
free(dup_str);

return 0;
}

函数名: stricmp
功 能: 以大小写不敏感方式比较两个串
用 法: int stricmp(char *str1, char *str2);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *buf1 = "BBB", *buf2 = "bbb";
int ptr;

ptr = stricmp(buf2, buf1);

if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");

if (ptr < 0)
printf("buffer 2 is less than buffer 1/n");

if (ptr == 0)
printf("buffer 2 equals buffer 1/n");

return 0;
}

函数名: strerror
功 能: 返回指向错误信息字符串的指针
用 法: char *strerror(int errnum);
程序例:

#include <stdio.h>
#include <errno.h>

int main(void)
{
char *buffer;
buffer = strerror(errno);
printf("Error: %s/n", buffer);
return 0;
}

函数名: strcmpi
功 能: 将一个串与另一个比较, 不管大小写
用 法: int strcmpi(char *str1, char *str2);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *buf1 = "BBB", *buf2 = "bbb";
int ptr;

ptr = strcmpi(buf2, buf1);

if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");

if (ptr < 0)
printf("buffer 2 is less than buffer 1/n");

if (ptr == 0)
printf("buffer 2 equals buffer 1/n");

return 0;
}

函数名: strncmp
功 能: 串比较
用 法: int strncmp(char *str1, char *str2, int maxlen);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)

{
char *buf1 = "aaabbb", *buf2 = "bbbccc", *buf3 = "ccc";
int ptr;

ptr = strncmp(buf2,buf1,3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");
else
printf("buffer 2 is less than buffer 1/n");

ptr = strncmp(buf2,buf3,3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 3/n");
else
printf("buffer 2 is less than buffer 3/n");

return(0);
}

函数名: strncmpi
功 能: 把串中的一部分与另一串中的一部分比较, 不管大小写
用 法: int strncmpi(char *str1, char *str2);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *buf1 = "BBBccc", *buf2 = "bbbccc";
int ptr;

ptr = strncmpi(buf2,buf1,3);

if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");

if (ptr < 0)
printf("buffer 2 is less than buffer 1/n");

if (ptr == 0)
printf("buffer 2 equals buffer 1/n");

return 0;
}

函数名: strncpy
功 能: 串拷贝
用 法: char *strncpy(char *destin, char *source, int maxlen);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char string[10];
char *str1 = "abcdefghi";

strncpy(string, str1, 3);
string[3] = '/0';
printf("%s/n", string);
return 0;
}

函数名: strnicmp
功 能: 不注重大小写地比较两个串
用 法: int strnicmp(char *str1, char *str2, unsigned maxlen);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *buf1 = "BBBccc", *buf2 = "bbbccc";
int ptr;

ptr = strnicmp(buf2, buf1, 3);

if (ptr > 0)
printf("buffer 2 is greater than buffer 1/n");

if (ptr < 0)
printf("buffer 2 is less than buffer 1/n");

if (ptr == 0)
printf("buffer 2 equals buffer 1/n");

return 0;
}

函数名: strnset
功 能: 将一个串中的所有字符都设为指定字符
用 法: char *strnset(char *str, char ch, unsigned n);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char *string = "abcdefghijklmnopqrstuvwxyz";
char letter = 'x';

printf("string before strnset: %s/n", string);
strnset(string, letter, 13);
printf("string after strnset: %s/n", string);

return 0;
}

函数名: strpbrk
功 能: 在串中查找给定字符集中的字符
用 法: char *strpbrk(char *str1, char *str2);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char *string1 = "abcdefghijklmnopqrstuvwxyz";
char *string2 = "onm";
char *ptr;

ptr = strpbrk(string1, string2);

if (ptr)
printf("strpbrk found first character: %c/n", *ptr);
else
printf("strpbrk didn't find character in set/n");

return 0;
}

函数名: strrchr
功 能: 在串中查找指定字符的最后一个出现
用 法: char *strrchr(char *str, char c);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char string[15];
char *ptr, c = 'r';

strcpy(string, "This is a string");
ptr = strrchr(string, c);
if (ptr)
printf("The character %c is at position: %d/n", c, ptr-string);
else
printf("The character was not found/n");
return 0;
}

函数名: strrev
功 能: 串倒转
用 法: char *strrev(char *str);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char *forward = "string";

printf("Before strrev(): %s/n", forward);
strrev(forward);
printf("After strrev(): %s/n", forward);
return 0;
}

函数名: strset
功 能: 将一个串中的所有字符都设为指定字符
用 法: char *strset(char *str, char c);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char string[10] = "123456789";
char symbol = 'c';

printf("Before strset(): %s/n", string);
strset(string, symbol);
printf("After strset(): %s/n", string);
return 0;
}

函数名: strspn
功 能: 在串中查找指定字符集的子集的第一次出现
用 法: int strspn(char *str1, char *str2);
程序例:

#include <stdio.h>
#include <string.h>
#include <alloc.h>

int main(void)
{
char *string1 = "1234567890";
char *string2 = "123DC8";
int length;

length = strspn(string1, string2);
printf("Character where strings differ is at position %d/n", length);
return 0;
}

函数名: strstr
功 能: 在串中查找指定字符串的第一次出现
用 法: char *strstr(char *str1, char *str2);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char *str1 = "Borland International", *str2 = "nation", *ptr;

ptr = strstr(str1, str2);
printf("The substring is: %s/n", ptr);
return 0;
}

函数名: strtod
功 能: 将字符串转换为double型值
用 法: double strtod(char *str, char **endptr);
程序例:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
char input[80], *endptr;
double value;

printf("Enter a floating point number:");
gets(input);
value = strtod(input, &endptr);
printf("The string is %s the number is %lf/n", input, value);
return 0;
}

函数名: strtok
功 能: 查找由在第二个串中指定的分界符分隔开的单词
用 法: char *strtok(char *str1, char *str2);
程序例:

#include <string.h>
#include <stdio.h>

int main(void)
{
char input[16] = "abc,d";
char *p;

/* strtok places a NULL terminator
in front of the token, if found */
p = strtok(input, ",");
if (p) printf("%s/n", p);

/* A second call to strtok using a NULL
as the first parameter returns a pointer
to the character following the token */
p = strtok(NULL, ",");
if (p) printf("%s/n", p);
return 0;
}

函数名: strtol
功 能: 将串转换为长整数
用 法: long strtol(char *str, char **endptr, int base);
程序例:

#include <stdlib.h>
#include <stdio.h>

int main(void)
{
char *string = "87654321", *endptr;
long lnumber;

/* strtol converts string to long integer */
lnumber = strtol(string, &endptr, 10);
printf("string = %s long = %ld/n", string, lnumber);

return 0;
}

函数名: strupr
功 能: 将串中的小写字母转换为大写字母
用 法: char *strupr(char *str);
程序例:

#include <stdio.h>
#include <string.h>

int main(void)
{
char *string = "abcdefghijklmnopqrstuvwxyz", *ptr;

/* converts string to upper case characters */
ptr = strupr(string);
printf("%s/n", ptr);
return 0;
}

函数名: swab
功 能: 交换字节
用 法: void swab (char *from, char *to, int nbytes);
程序例:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

char source[15] = "rFna koBlrna d";
char target[15];

int main(void)
{
swab(source, target, strlen(source));
printf("This is target: %s/n", target);
return 0;
}

常用函数源码

很多人认为C语言中的难点是指针,对指针的理解直接关系到所编程序的好坏,所以,
在这里列举了一些C编译器通常都有的标准函数的源代码,看过它们,就能对指针和字符串
有所了解了.
1. strlen(),计算字符串长度
int strlen(const char string)
{
int i=0;
while(string[i]) i++;
return i;
}
2. strcpy(), 字符串拷贝.
char *strcpy(char *destination, const char *source)
{
while(*destinaton++=*source++);
return (destination-1);
}
3. strcat(), 字符串的连接.
char *strcat(char *target,const char *source)
{
char *original=target;
while(*target) target++; // Find the end of the string
while(*target++=*source++);
return(original);
}
4. streql(), 判断两个字符串是否相等.
int streql(char *str1,char *str2)
{
while((*str1==*str2)&&(*str1))
{
str1++;
str2++;
}
return((*str1==NULL)&&(*str2==NULL));
}
5. strchr(), 在字符串中查找某个字符.
char *strchr(const char *string,int letter)
{
while((*string!=letter)&(*string))
string++;
return (string);
}
6. chrcnt(), 计算某个字符在字符串中出现的次数.
int chrcnt(const char *string,int letter)
{
int count=0;
while(*string)
if(*string==letter)count++;
return count;
}
7. strcmp(), 判断两个字符串是否相等.
int strcmp(const char *str1,const char *str2)
{
while((*str1==*str2)&&(*str1))
{
str1++;
str2++;
}
if((*str1==*str2)&&(!*str1)) //Same strings
return o;
else if((*str1)&&(!*str2)) //Same but str1 longer
return -1;
else if((*str2)&&(!*str1)) //Same but str2 longer
else
return((*str1>*str2)?-1:1);
}

2、strcmp函数：

int mystrcmp(const char *str1,const char *str2)
{
while((*str1==*str2)&&(*str1))
{
str1++;
str2++;
}
if((*str1==*str2)&&(!*str1)) //Same strings
return 0;
else if((*str1)&&(!*str2)) //Same but str1 longer
return 1;
else if ((!*str1)&&(*str2))
return -1 ;
else
return ((*str1>*str2)?1:-1);

}

3、strcat函数：

char *mystrcat(char *target,const char *source)
{
char *original=target;
while(*target) target++; // Find the end of the string
while(*target++=*source++);
return(original);
}

int main(void)
{

char destination[25];
char * cc;
char *blank = " ", *c = "C++", *Borland = "Borland";
strcpy(destination, Borland);
mystrcat(destination, blank);
cc=mystrcat(destination, c);
printf("%s/n", cc);

}
4、strcpy函数

char *mystrcpy(char *destination, const char *source)
{
while(*destination++=*source++);
return (destination);
}

5、strlen函数
int mystrlen(const char *string)
{
int i=0;
while(*string++)
i++;
return i;
}
5、streql函数
int mystreql(char *str1,char *str2)
{
while((*str1==*str2)&&(*str1))
{
str1++;
str2++;
}
return((*str1==NULL)&&(*str2==NULL));
}
6、strchr函数
char * mystrchr(const char *string,char letter)
{
while((*string!=letter)&&(*string))
string++;
return (string);
}

int main(void)
{
char string[15];
char *ptr, c = 'r';
strcpy(string, "This is a string");
ptr = mystrchr(string, c);

if (ptr)
printf("The character %c is at position: %d/n", c,ptr-string);
else
printf("The character was not found/n");
return 0;
}
7、ctrcnt函数
int mychrcnt(const char *string,char letter) /*指定计算字符串内的指定字符的个数*/
{
int count=0;

while(*string)
{
if(*string==letter)
count++;
string++;
}
return count;
}

函数strcpy的实现源代码
　　char *strcpy(char *strDest, const char *strSrc);
　　{
　　assert((strDest!=NULL) && (strSrc !=NULL));
　　char *address = strDest;
　　while( (*strDest++ = * strSrc++) != ‘/0’ )
　　NULL ;
　　return address ;
　　}

函数strcat的实现源代码
char * strcat(char * dest, const char * src)
{
char *tmp = dest;

while (*dest)
dest++;
while ((*dest++ = *src++) != '/0')
;

return tmp;
}

函数原型：int strcmp(const char *dest, const char *source) ;

返回值：返回整数值，如果dest > source,则返回值大于0，如果dest = source,则返回值等于0，如果dest < source ,则返回值小于0。字符大小是按照字符的字典序列进行排列的。

参数说明：都是以''/0''为结束符的字符串

函数strcmp的实现源代码
int strcmp(const char *dest, const char *source)
{
assert((NULL != dest) && (NULL != source));
while (*dest && *source && (*dest == *source))
{
dest ++;
source ++;
}
return *dest - *source;
/*如果dest > source,则返回值大于0，如果dest = source,则返回值等于0，如果dest < source ,则返回值小于0。*/
}

函数memset的实现源代码
void* memcpy( void* dest, const void* src, size_t count )
{

if (count<0)

{printf("Invalid count number !./n");

return (void*)0;}

if(src==NULL||dest==NULL)

return (void*)0 ;

if ((unsigned int)dest==(unsigned int)src)

{printf("The source is equal with the destanation!./n");

return dest;}

char* d = (char*)dest;
const char* s = (const char*)src;
while(count--)
*d++ = *s++;
return dest;
}

函数memset的实现源代码
void* memcpy( void* dest, const void* src, size_t count )
{

if (count<0)

{printf("Invalid count number !./n");

return (void*)0;}

if(src==NULL||dest==NULL)

return (void*)0 ;

if ((unsigned int)dest==(unsigned int)src)

{printf("The source is equal with the destanation!./n");

return dest;}

char* d = (char*)dest;
const char* s = (const char*)src;
while(count--)
*d++ = *s++;
return dest;
}

函数strlen的实现源代码
　　int strlen(const char *str)

　　{

　　assert(str != NULL);

　　int len = 0;

　　while((*str++) != '/0')

　　len++;

　　return len;

　　}

函数malloc的实现源代码

引用：http://topic.csdn.net/t/20051114/18/4392766.html

#ifndef CRAY
#define STACKMIN 512
#define MINBLK (2*sizeof(struct mem) + 16)
#define F _malloc_free_
#define SBGULP 8192
#include "string.h" /* for memcpy */

#ifdef KR_headers
#define Char char
#define Unsigned unsigned
#define Int /*int*/
#else
#define Char void
#define Unsigned size_t
#define Int int
#endif

typedef struct mem {
struct mem *next;
Unsigned len;
} mem;

mem *F;

Char *
#ifdef KR_headers
malloc(size)
register Unsigned size;
#else
malloc(register Unsigned size)
#endif
{
register mem *p, *q, *r, *s;
unsigned register k, m;
extern Char *sbrk(Int);
char *top, *top1;

size = (size+7) & ~7;
r = (mem *) &F;
for (p = F, q = 0; p; r = p, p = p->next) {
if ((k = p->len) >= size && (!q || m > k)) {
m = k;
q = p;
s = r;
}
}
if (q) {
if (q->len - size >= MINBLK) { /* split block */
p = (mem *) (((char *) (q+1)) + size);
p->next = q->next;
p->len = q->len - size - sizeof(mem);
s->next = p;
q->len = size;
}
else
s->next = q->next;
}
else {
top = (Char *)(((long)sbrk(0) + 7) & ~7);
if (F && (char *)(F+1) + F->len == top) {
q = F;
F = F->next;
}
else
q = (mem *) top;
top1 = (char *)(q+1) + size;
if (sbrk((int)(top1-top+SBGULP)) == (Char *) -1)
return 0;
r = (mem *)top1;
r->len = SBGULP - sizeof(mem);
r->next = F;
F = r;
q->len = size;
}
return (Char *) (q+1);
}

void
#ifdef KR_headers
free(f)
Char *f;
#else
free(Char *f)
#endif
{
mem *p, *q, *r;
char *pn, *qn;

if (!f) return;
q = (mem *) ((char *)f - sizeof(mem));
qn = (char *)f + q->len;
for (p = F, r = (mem *) &F; ; r = p, p = p->next) {
if (qn == (Char *) p) {
q->len += p->len + sizeof(mem);
p = p->next;
}
pn = p ? ((char *) (p+1)) + p->len : 0;
if (pn == (Char *) q) {
p->len += sizeof(mem) + q->len;
q->len = 0;
q->next = p;
r->next = p;
break;
}
if (pn < (char *) q) {
r->next = q;
q->next = p;
break;
}
}
}

Char *
#ifdef KR_headers
realloc(f, size)
Char *f;
Unsigned size;
#else
realloc(Char *f, Unsigned size)
#endif
{
mem *p;
Char *q, *f1;
Unsigned s1;

if (!f) return malloc(size);
p = (mem *) ((char *)f - sizeof(mem));
s1 = p->len;
free(f);
if (s1 > size)
s1 = size + 7 & ~7;
if (!p->len) {
f1 = (Char *)(p->next + 1);
memcpy(f1, f, s1);
f = f1;
}
q = malloc(size);
if (q && q != f)
memcpy(q, f, s1);
return q;
}

/* The following (calloc) should really be in a separate file, */
/* but defining it here sometimes avoids confusion on systems */
/* that do not provide calloc in its own file. */

Char *
#ifdef KR_headers
calloc(n, m) Unsigned m, n;
#else
calloc(Unsigned n, Unsigned m)
#endif
{
Char *rv;
rv = malloc(n *= m);
if (n && rv)
memset(rv, 0, n);
return rv;
}
#endif