Strlen (); strcpy (); Strcat (); STRCMP ()---Notes

Pointers Small Knowledge Points:

int a = 10;

int *p=&a;

int *q=p; The address of A is saved in P

int *q=p; Assigning the value of p to the Q function is to let Q also point to a

Strlen (); To find the length of a string

strcpy (); Copy string

Strcat (); Connection string

strcmp (); Comparison of string sizes

1typedef unsignedintsize_t2 3size_t My_strlen (Const Char*str)//strlen ()4 {5ASSERT (str!=NULL);6      intlen=0;7       while(*str! =' /')    8      {9len++;Tenstr++; One      } A        returnLen; - } -  the //recursion is not used with intermediate variables; -size_t My_strlen (Const Char*str) - { -ASSERT (str!=NULL); +       if(*str==' /') -              return 0; +       Else A           returnMy_strlen (++STR) +1;  at}

1 Char* MY_STRCPY (Char*dest,Const Char*src)//strcpy ()2 {3ASSERT (dest!=null&&src!=NULL);4      Char*dest_tmp=dest;//Protection Parameters5      Const Char*SRC_TMP=SRC;//type Match6       while(*src_tmp!=' /')7     {8*dest_tmp++=*src_tmp++;9      }Ten  One*dest_tmp=' /'; A            returndest; - } -  the voidMain () - { -       Chars1[ -]; -       Char*S2 ="ABCDE"; + my_strcpy (S1, S2); -cout<<"S1 ="<<s1<<endl;//ABCDE//c++ Output mode + } A //or a third party accepts at voidMain () - { -       Chars1[ -]; -       Char*S2 ="ABCDE"; -       Char*s3=my_strcpy (S1, S2); -cout<<"s3 ="<<s3<<endl;//ABCDE in}

1 Char* MY_STRCAT (Char*dest,Const Char*src)//strcat ()2 {3ASSERT (src!=null&&dest!=NULL)4   Char*dest_tmp=dest;//Protection Parameters5   Const Char*SRC_TMP=SRC;//type Match6   7     while(*dest_tmp!=' /') 8dest_tmp++;9     while(*src_tmp!=' /')Ten*dest_tmp++=*src_tmp++; One*dest_tmp=' /'; A returndest; - } -  the voidMain () - { -     Chars1[ -] ="abcdef"; -     Chars2[ -] ="Ghijk"; +     Char*STR1 =my_strcat (S1, S2); -cout<<"S1 ="<<s1<<Endl; +cout<<"str1 ="<<str1<<endl;//Abcdefghijk//c++ Output mode A  at}

1 /*strcmp (S1,S2); 2 s1>s2: Return 13 S1=s2: return 04 S1<S2: Return-15 */6 7 intMY_STRCMP (Const Char*STR1,Const Char*str2)//strcmp ()8 {9ASSERT (Str1!=null && str2!=NULL);Ten     if(*str1==' /'&& *str2==' /') One         return 0; A      while(*str1!=' /'&& *str2!=' /') -     { -         if(*str1 > *str2) the             return 1; -         Else if(*str1 < *str2) -             return-1; -str1++; +str2++; -     } +     if(*str1==' /'&& *str2!=' /') A         return-1; at     if(*str1!=' /'&& *str2==' /') -         return 1; -     return 0; - } -  - //or in intMY_STRCMP (Const Char*STR1,Const Char*str2) - { toASSERT (Str1!=null && str2!=NULL); +     intresult =0; -      while(*str1!=' /'|| *str2!=' /') the     { *         if(result = *STR1-*STR2)! =0 ) $              Break;Panax Notoginsengstr1++; -str2++; the     } +     if(Result >0 ) Aresult =1; the     Else if(Result <0 ) +result =-1; -     returnresult; $}

Attention:

1, the validity of judging parameters;

(assertion) The argument passed cannot be null.

2, if need to return the pointer, the use of intermediate variables;

my_strcpy (); My_strcat ();

3. Ensure sufficient space

my_strcpy (); My_strcat ();

4, parameter protection to ensure that the parameters are not modified inside the function

Strlen (); strcpy (); Strcat (); STRCMP ()---Notes