[收藏備用]C語言字串處理函數

函數名: strcpy
功  能: 拷貝一個字串到另一個
用  法: char *stpcpy(char *destin, char *source);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
   char string[10];
   char *str1 = "abcdefghi";
   stpcpy(string, str1);
   printf("%sn", string);
   return 0;
}
 
 
 
函數名: strcat
功  能: 字串拼接函數
用  法: char *strcat(char *destin, char *source);
程式例:
#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("%sn", destination);
   return 0;
}
 
 
 
函數名: strchr
功  能: 在一個串中尋找給定字元的第一個匹配之處
用  法: char *strchr(char *str, char c);
程式例:
#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: %dn", c, ptr-string);
    else
       printf("The character was not foundn");
    return 0;
}
 
 
 
函數名: strcmp
功  能: 串比較
用  法: int strcmp(char *str1, char *str2);
看Asic碼，str1>str2，傳回值 > 0；兩串相等，返回0
程式例:
#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 1n");
    else
       printf("buffer 2 is less than buffer 1n");
    ptr = strcmp(buf2, buf3);
    if (ptr > 0)
       printf("buffer 2 is greater than buffer 3n");
    else
       printf("buffer 2 is less than buffer 3n");
    return 0;
}
 
 
 
函數名: strncmpi
功  能: 將一個串中的一部分與另一個串比較, 不管大小寫
用  法: int strncmpi(char *str1, char *str2, unsigned maxlen);
程式例:
#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 1n");
   if (ptr < 0)
      printf("buffer 2 is less than buffer 1n");
   if (ptr == 0)
      printf("buffer 2 equals buffer 1n");
   return 0;
}
 
 
 
函數名: strcpy
功  能: 串拷貝
用  法: char *strcpy(char *str1, char *str2);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
    char string[10];
    char *str1 = "abcdefghi";
    strcpy(string, str1);
    printf("%sn", string);
    return 0;
}
 
 
 
函數名: strcspn
功  能: 在串中尋找第一個給定字元集內容的段
用  法: int strcspn(char *str1, char *str2);
程式例:
#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 %dn", length);
    return 0;
}
 
 
 
函數名: strdup
功  能: 將串拷貝到建立的位置處
用  法: char *strdup(char *str);
程式例:
#include <stdio.h>
#include <string.h>
#include <alloc.h>
int main(void)
{
    char *dup_str, *string = "abcde";
    dup_str = strdup(string);
    printf("%sn", dup_str);
    free(dup_str);
    return 0;
}
 
 
 
函數名: stricmp
功  能: 以大小寫不敏感方式比較兩個串
用  法: int stricmp(char *str1, char *str2);
程式例:
#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 1n");
   if (ptr < 0)
      printf("buffer 2 is less than buffer 1n");
   if (ptr == 0)
      printf("buffer 2 equals buffer 1n");
   return 0;
}
 
 
函數名: strerror
功  能: 返回指向錯誤資訊字串的指標
用  法: char *strerror(int errnum);
程式例:
#include <stdio.h>
#include <errno.h>
int main(void)
{
   char *buffer;
   buffer = strerror(errno);
   printf("Error: %sn", buffer);
   return 0;
}
 
 
 
函數名: strcmpi
功  能: 將一個串與另一個比較, 不管大小寫
用  法: int strcmpi(char *str1, char *str2);
程式例:
#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 1n");
   if (ptr < 0)
      printf("buffer 2 is less than buffer 1n");
   if (ptr == 0)
      printf("buffer 2 equals buffer 1n");
   return 0;
}
 
 
 
函數名: strncmp
功  能: 串比較
用  法: int strncmp(char *str1, char *str2, int maxlen);
程式例:
#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 1n");
   else
      printf("buffer 2 is less than buffer 1n");
   ptr = strncmp(buf2,buf3,3);
   if (ptr > 0)
      printf("buffer 2 is greater than buffer 3n");
   else
      printf("buffer 2 is less than buffer 3n");
   return(0);
}
 
 
函數名: strncmpi
功  能: 把串中的一部分與另一串中的一部分比較, 不管大小寫
用  法: int strncmpi(char *str1, char *str2);
程式例:
#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 1n");
   if (ptr < 0)
      printf("buffer 2 is less than buffer 1n");
   if (ptr == 0)
      printf("buffer 2 equals buffer 1n");
   return 0;
}
 
 
函數名: strncpy
功  能: 串拷貝
用  法: char *strncpy(char *destin, char *source, int maxlen);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
   char string[10];
   char *str1 = "abcdefghi";
   strncpy(string, str1, 3);
   string[3] = '';
   printf("%sn", string);
   return 0;
}
 
 
函數名: strnicmp
功  能: 不注重大小寫地比較兩個串
用  法: int strnicmp(char *str1, char *str2, unsigned maxlen);
程式例:
#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 1n");
   if (ptr < 0)
      printf("buffer 2 is less than buffer 1n");
   if (ptr == 0)
      printf("buffer 2 equals buffer 1n");
   return 0;
}
 
 
 
函數名: strnset
功  能: 將一個串中的所有字元都設為指定字元
用  法: char *strnset(char *str, char ch, unsigned n);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
   char *string = "abcdefghijklmnopqrstuvwxyz";
   char letter = 'x';
   printf("string before strnset: %sn", string);
   strnset(string, letter, 13);
   printf("string after  strnset: %sn", string);
   return 0;
}
 
 
函數名: strpbrk
功  能: 在串中尋找給定字元集中的字元
用  法: char *strpbrk(char *str1, char *str2);
程式例:
#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: %cn", *ptr);
   else
      printf("strpbrk didn't find character in setn");
   return 0;
}
 
 
 
函數名: strrchr
功  能: 在串中尋找指定字元的最後一個出現
用  法: char *strrchr(char *str, char c);
程式例:
#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: %dn", c, ptr-string);
   else
      printf("The character was not foundn");
   return 0;
}
 
 
 
函數名: strrev
功  能: 串倒轉
用  法: char *strrev(char *str);
程式例:
#include <string.h>
#include <stdio.h>
int main(void)
{
   char *forward = "string";
   printf("Before strrev(): %sn", forward);
   strrev(forward);
   printf("After strrev():  %sn", forward);
   return 0;
}
 
函數名: strset
功  能: 將一個串中的所有字元都設為指定字元
用  法: char *strset(char *str, char c);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
   char string[10] = "123456789";
   char symbol = 'c';
   printf("Before strset(): %sn", string);
   strset(string, symbol);
   printf("After strset():  %sn", string);
   return 0;
}
 
 
 
函數名: strspn
功  能: 在串中尋找指定字元集的子集的第一次出現
用  法: int strspn(char *str1, char *str2);
程式例:
#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 %dn", length);
   return 0;
}
 
 
函數名: strstr
功  能: 在串中尋找指定字串的第一次出現
用  法: char *strstr(char *str1, char *str2);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
   char *str1 = "Borland International", *str2 = "nation", *ptr;
   ptr = strstr(str1, str2);
   printf("The substring is: %sn", ptr);
   return 0;
}
 
 
函數名: strtod
功  能: 將字串轉換為double型值
用  法: double strtod(char *str, char **endptr);
程式例:
#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 %lfn", input, value);
   return 0;
}
 
 
 
函數名: strtok
功  能: 尋找由在第二個串中指定的分界符分隔開的單詞
用  法: char *strtok(char *str1, char *str2);
程式例:
#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("%sn", 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("%sn", p);
   return 0;
}
 
 
 
函數名: strtol
功  能: 將串轉換為長整數
用  法: long strtol(char *str, char **endptr, int base);
程式例:
#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 = %ldn", string, lnumber);
   return 0;
}
 
函數名: strupr
功  能: 將串中的小寫字母轉換為大寫字母
用  法: char *strupr(char *str);
程式例:
#include <stdio.h>
#include <string.h>
int main(void)
{
   char *string = "abcdefghijklmnopqrstuvwxyz", *ptr;
   /* converts string to upper case characters */
   ptr = strupr(string);
   printf("%sn", ptr);
   return 0;
}
 
 
 
函數名: swab
功  能: 交換位元組
用  法: void swab (char *from, char *to, int nbytes);
程式例:
#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: %sn", target);
   return 0;
}

PS:isalpha()是字元函數，不是字串函數，

isalpha
 

  原型：extern int isalpha(int c);
 
  用法：#include <ctype.h>
 
  功能：判斷字元c是否為英文字母
 
  說明：當c為英文字母a-z或A-Z時，返回非零值，否則返回零。
 
  舉例：

      // isalpha.c
     
      #include <syslib.h>
      #include <ctype.h>
      #include <stdio.h>

      main()
      {
        int c;
       
        clrscr();        // clear screen
        printf("Press a key");
        for(;;)
        {
          c=getchar();
          clrscr();
          printf("%c: %s letter",c,isalpha(c)?"is":"not");
        }
        return 0; // just to avoid warnings by compiler
      }