C:字符串操作

2008-05-12 21:44:59

1.字符串连接

/*append string t to the end of string s*/
void strapd(char *s,char *t)
{
    while(*s)
      s++;
    while(*t)
      *s++=*t++;
    *s='\0';
}

2.字符串长度

/*return the length of string s*/
int strlen(const char *s)
{
    const char *cptr=s;
    while(*s)
      s++;
    return s-cptr;
}

3.字符串判等

#define TRUE 1
#define FALSE 0
/*return 1 for equals between string s and strng t*/
/*return 0 for not equals */
int streql(const char *s,const char *t)
{
    while(*s==*t && *s && *t){
        s++;
        t++;
    }
    if(!*s && !*t)
      return TRUE;
    else
      return FALSE;
}

4.字符串尾匹配

#define TRUE 1
#define FALSE 0
/*if found string t at the end of string s,return 1*/
/*else return 0*/
int strend(char *s,char *t)
{
    char *bs=s;     /*begining of s*/
    char *bt=t;     /*begining of t*/

    while(*s)       /*end of s*/
      s++;
    while(*t)       /*end of t*/
      t++;
    for(;*s==*t;s--,t--)
      if(t==bt||s==bs)
        break;      /*reach the begining*/
    if(*s==*t && t==bt && *s)
      return TRUE;
    return FALSE;
}

5.将匹配的单个字符从源字符串中删除

/*remove all char c from string s*/
void charrm(char *s, int c)
{
    char *tar;

    tar=s;
    for(;*s;s++)
      if(*s !=c)
        *tar++=*s;
    *tar='\0';
}

6.将匹配的字符串从源字符串中删除

/*remove all string c from string s*/
void strrm(char *s,char *c)
{
    char *tar;
    char *bms;    /*beginning position for matching*/
    char *bc;    /*begining of c*/

    tar=s;
    for(;*s;s++){
        if(*s !=*c)
          *tar++=*s;
        else{
            bms=s;
            bc=c;
            /*begin macthing*/
            for(;*bc && *s && *s==*bc;s++,bc++)
              ;
            if(!*bc) /*matched*/
                s--;/*for the last s++ in loop for above*/
            else if(!*s) {/*unmatched and will never be matched*/
                for(;*bms;bms++)
                  *tar++=*bms;
                *tar='\0';
                return;
            }
            else/*unmatched*/
              s=bms;
        }
    }
    *tar='\0';
}

7.扩展字符串
将类似于a-z之类的速记符号扩展为abc...xyz(26个字母).扩展的依据是字符在ASCII中的顺序.

/*expand shortand notation in string s into string t*/
/*a-e:abcde*/
void strepd(char *s,char *t)
{
    char c;

    while((c=*s++)!='\0')
      if(*s =='-' && *++s >=c){
          while(c<*s)  /*expand*/
            *t++=c++;
      }else
        *t++=c;
    *t='\0';
}

8.返回首个匹配字符串的位置

/*return the leftest position of string t in string s */
int strlidx(char *s,char *t)
{
    char *bs;    /*begining of s*/
    char *bms;   /*begining position for matching*/
    char *bt;    /*begining of t*/

    bs=s;
    for(;*s;s++)
        if(*s==*t){
          bms=s;
          bt=t;
          for(;*bt && *s && *s==*bt;bt++,s++)
            ;
          if(!*bt) /*matched*/
            return bms-bs;
          else if (!*s)/*unmatched and will never be matched*/
            return -1;
          else /*unmatched*/
            s=bms;
        }
    return -1;
}

9.返回末个匹配字符串的位置

/*return the rightest position of t in s */
int strridx(char *s,char *t)
{
    char *es;   /*end of s*/
    char *et;   /*end of t*/
    char *emt;  /*end position for matching in t*/
    char *ems;  /*end position for matching in s*/

    es=s;
    while(*es)       /*end of s*/
      es++;
    es--;            /*exclude '\0'*/
    et=t;
    while(*et)       /*end of t*/
      et++;
    et--;           /*exclude '\0'*/

    for(;es!=s;es--)
        if(*es==*et){
          emt=et;
          ems=es;
          for(;*es==*emt;es--,emt--){
            if(emt==t||es==s)
              break;
          }
          if(*es==*emt && emt==t && *es)/*matched*/
            return es-s;
          else if(es==s)/*unmatched and will never be matched*/
            return -1;
          else /*unmatched*/
            es=ems;
          }
    return -1;
}

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C:字符串操作

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