COPY CHAR ONE BY ONE

博主分享了自己初次编写ASM程序的经验,通过循环方式实现字符串'ABCD'的复制,过程中遇到了拼写错误并进行了调试,强调了动手实践的重要性。

从没完整写过一个asm程序,今天写了个练手,有两个拼写错误,还调试了半天 以后看来要多动手。

copy字符串ABCD到指定位置,采用循环,也可用串操作。 

;COPY.ASM
;FUNCTION:COPY CHAR ONE BY ONE
;AUTHOR:MAX0301

DSEG SEGMENT
    D1 DB 
'ABCD'
DSEG ENDS
;

ESEG SEGMENT
    D2 DB 
4 DUP(?)
ESEG ENDS
;

CSEG SEGMENT
    ASSUME CS:CSEG,DS:DSEG,ES:ESEG
START:MOV AX,DSEG
      MOV DS,AX
      MOV AX,ESEG
      MOV ES,AX
      MOV SI,OFFSET D1
      MOV DI,OFFSET D2
      MOV CX,
4
COPY:MOV AL,[SI]
     MOV ES:[DI],AL
     INC SI
     INC DI
     DEC CX
     JNZ COPY
     MOV AH,4CH
     INT 21H
CSEG ENDS
     END START   
### Char Pointer in C Programming In C programming, a `char` pointer is commonly used for handling strings and character arrays. A string in C is essentially an array of characters terminated by a null character (`'\0'`). The use of pointers allows efficient manipulation of such arrays without the need to copy large amounts of data[^4]. A `char` pointer can be initialized to point to a string literal, as shown below: ```c char *str = "Hello, World!"; ``` This approach initializes a pointer to point to the first character of the string. It is important to note that string literals are typically stored in read-only memory, so attempting to modify them through the pointer may lead to undefined behavior. Pointers also enable functions to manipulate strings directly in memory. For example, a function can accept a `char` pointer as an argument and modify the contents of the string it points to. This is particularly useful when implementing string manipulation functions like converting all lowercase letters to uppercase, as demonstrated in the provided code snippet. Here’s how such a function might look: ```c char *upper(char *str) { char *dest = str; while (*str != '\0') { if (*str >= 'a' && *str <= 'z') { *str -= 'a' - 'A'; } str++; } return dest; } ``` When dealing with `char` pointers, understanding pointer arithmetic is crucial. For instance, incrementing a `char` pointer moves it to the next character in the array, effectively stepping through each byte since the size of a `char` is one byte. This property makes `char` pointers especially useful for iterating over arrays, processing strings, and dynamically allocating memory for character buffers[^3]. Memory allocation for structures containing `char` pointers requires careful consideration. When defining a structure that includes a `char` pointer, the programmer must ensure sufficient memory is allocated for the data the pointer will eventually reference. Additionally, proper deallocation is necessary to prevent memory leaks[^3]. #### Example Usage Here's an example of using a `char` pointer within a main function to process input: ```c #include <stdio.h> int main() { char c[20]; printf("Please input the strings\n"); gets(c); // Note: Use fgets instead for safer input handling printf("Before upper, the strings are: \n %s\n", c); char *dest = upper(c); printf("After upper, the strings are: \n %s\n", dest); return 0; } ``` This example demonstrates reading a string from standard input, modifying it in place via a function that accepts a `char` pointer, and then printing the modified string[^4]. #### Summary Using `char` pointers in C provides a powerful mechanism for working with strings and character data efficiently. They allow direct manipulation of memory, which is essential for performance-critical applications. However, this power comes with responsibility, requiring careful management of memory allocation and ensuring that operations do not exceed the bounds of allocated memory[^2].
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