C语言--字符串操作函数及其使用

strcpy

• 函数名: strcpy
• 功 能: 拷贝一个字符串到另一个
• 声 明: char *strcpy(char *dst, const char *src);
  程序实现：

char * strcpy(char *dst,const char *src)   
{
    if((dst==NULL)||(src==NULL))

           return NULL; 

    char *ret = dst; //[1]

    while ((*dst++=*src++)!='\0'); //[2]

    return ret;//[3]
}

• （1）const 修饰：源字符串参数用const修饰，防止修改源字符串；
• （2）空指针检查：源指针和目的指针都有可能会出现空指针的情况，所以应该对其进行检查；
• （3）为什么要设置ret 指针以及返回ret指针的位置[3]，由于目的指针dst已经在进行移动了，所以用辅助指针ret表明首指针；
• （4）以上所示[2]处，为简单的字符串的复制过程，正好表明strcpy函数遇到’\0’将会停止；

程序例程:

#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: 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; 
}