c字符串函数底层实现

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1、C字符串函数底层实现1/*2 * linux/lib/string.c3 *4 * Copyright(C)1991,1992 LinusTorvalds5 */67/*8 *stupidlibraryroutines..Theoptimizedversionsshouldgenerallybefound9 *asinlinecodein10 *11 *Thesearebuggyaswell..12 */13 14#include1516char*___st

2、rtok=NULL;1718char*strcpy(char*dest,constchar*src)19{20        char*tmp=dest;2122        while((*dest++=*src++)!='')23                /*nothing*/;24        returntmp;25}2627char*strncpy(char*dest,constchar*src,size_tcount)28{29        char*tmp=dest;3031        

3、while(count--&&(*dest++=*src++)!='')32                /*nothing*/;3334        returntmp;35}3637char*strcat(char*dest,constchar*src)38{39        char*tmp=dest;4041        while(*dest)42                dest++;43        while((*dest++=*src++)!='')44             

4、   ;4546        returntmp;47}4849char*strncat(char*dest,constchar*src,size_tcount)50{51        char*tmp=dest;5253        if(count){54                while(*dest)55                        dest++;56                while((*dest++=*src++)){57                        i

5、f(--count==0)58                                break;59                }60        }6162        returntmp;63}6465intstrcmp(constchar*cs,constchar*ct)66{67        registersignedchar__res;6869        while(1){70                if((__res=*cs-*ct++)!=0

6、

7、!*cs++)71     

8、                   break;72        }7374        return__res;75}7677intstrncmp(constchar*cs,constchar*ct,size_tcount)78{79        registersignedchar__res=0;8081        while(count){82                if((__res=*cs-*ct++)!=0

9、

10、!*cs++)83                        break;8

11、4                count--;85        }8687        return__res;88}8990char*strchr(constchar*s,charc)91{92        for(;*s!=c;++s)93                if(*s=='')94                        returnNULL;95        return(char*)s;96}9798size_tstrlen(constchar*s)99{100        

12、constchar*sc;101102        for(sc=s;*sc!='';++sc)103                /*nothing*/;104        returnsc-s;105}106107size_tstrnlen(constchar*s,size_tcount)108{109