Delphi Copy 函数 和 Pos函数

1、copy（a,b,c);  -- 复制指定的字符串

• a：就是copy源，就是一个字符串，表示你将要从a里copy一些东西，
• b：从a中的第b位开始copy（包含第1位），
• c：copy从第b位开始后的c个字符，

示例：　

m:='the fellowship of the ring'
s：=copy（m,2,2）；                           //s值为‘he’

函数原型：

procedure       _Copy{ s : ShortString; index, count : Integer ) : ShortString};
asm
{     ->EAX     Source string                   }
{       EDX     index                           }
{       ECX     count                           }
{       [ESP+4] Pointer to result string        }

        PUSH    ESI
        PUSH    EDI

        MOV     ESI,EAX
        MOV     EDI,[ESP+8+4]

        XOR     EAX,EAX
        OR      AL,[ESI]
        JZ      @@srcEmpty

{       limit index to satisfy 1 <= index <= Length(src) }

        TEST    EDX,EDX
        JLE     @@smallInx
        CMP     EDX,EAX
        JG      @@bigInx
@@cont1:

{       limit count to satisfy 0 <= count <= Length(src) - index + 1    }

        SUB     EAX,EDX { calculate Length(src) - index + 1     }
        INC     EAX
        TEST    ECX,ECX
        JL      @@smallCount
        CMP     ECX,EAX
        JG      @@bigCount
@@cont2:

        ADD     ESI,EDX

        MOV     [EDI],CL
        INC     EDI
        REP     MOVSB
        JMP     @@exit

@@smallInx:
        MOV     EDX,1
        JMP     @@cont1
@@bigInx:
{       MOV     EDX,EAX
        JMP     @@cont1 }
@@smallCount:
        XOR     ECX,ECX
        JMP     @@cont2
@@bigCount:
        MOV     ECX,EAX
        JMP     @@cont2
@@srcEmpty:
        MOV     [EDI],AL
@@exit:
        POP     EDI
        POP     ESI
    RET 4
end;

 

2、pos(a,b);   -- 取出子串a，在父串b中第一次出现的位置； 

示例：

pos（'b'，'abcd'）；  //返回结果  2；     

函数原型：

procedure       _Pos{ substr : ShortString; s : ShortString ) : Integer};
asm
{     ->EAX     Pointer to substr               }
{       EDX     Pointer to string               }
{     <-EAX     Position of substr in s or 0    }

        PUSH    EBX
        PUSH    ESI
        PUSH    EDI

        MOV     ESI,EAX { Point ESI to substr           }
        MOV     EDI,EDX { Point EDI to s                }

        XOR     ECX,ECX { ECX = Length(s)               }
        MOV     CL,[EDI]
        INC     EDI             { Point EDI to first char of s  }

        PUSH    EDI             { remember s position to calculate index        }

        XOR     EDX,EDX { EDX = Length(substr)          }
        MOV     DL,[ESI]
        INC     ESI             { Point ESI to first char of substr     }

        DEC     EDX             { EDX = Length(substr) - 1              }
        JS      @@fail  { < 0 ? return 0                        }
        MOV     AL,[ESI]        { AL = first char of substr             }
        INC     ESI             { Point ESI to 2'nd char of substr      }

        SUB     ECX,EDX { #positions in s to look at    }
                        { = Length(s) - Length(substr) + 1      }
        JLE     @@fail
@@loop:
        REPNE   SCASB
        JNE     @@fail
        MOV     EBX,ECX { save outer loop counter               }
        PUSH    ESI             { save outer loop substr pointer        }
        PUSH    EDI             { save outer loop s pointer             }

        MOV     ECX,EDX
        REPE    CMPSB
        POP     EDI             { restore outer loop s pointer  }
        POP     ESI             { restore outer loop substr pointer     }
        JE      @@found
        MOV     ECX,EBX { restore outer loop counter    }
        JMP     @@loop

@@fail:
        POP     EDX             { get rid of saved s pointer    }
        XOR     EAX,EAX
        JMP     @@exit

@@found:
        POP     EDX             { restore pointer to first char of s    }
        MOV     EAX,EDI { EDI points of char after match        }
        SUB     EAX,EDX { the difference is the correct index   }
@@exit:
        POP     EDI
        POP     ESI
        POP     EBX
end;

延伸查看PosEx函数　　

　　

 

创建时间：2020.07.05　　更新时间：2020.08.17　　2022.05.06