Question

I am trying to

• take two strings (message1, message2),
• assign str1 to message1 if message1 and message2 are empty,
• assign str2 to message2 if it is empty and message1 is full,
• and save message 2 over message 1 and put message2 == message3 if both message1 and message2 were full.

I get weird results as shown. But memcpy is not working. (I know it’s my fault somehow.)

input

message1: ffW
message 2: a
message 3 (2 writes over 1, 3 writes over 2): bbb

MESSAGE 1a: ffW 
MESSAGE 2a: a_W 
MESSAGE 1ab: a_W 
MESSAGE 2ab: a_W 
MESSAGE 1b: a_W 
MESSAGE 2b: bbb 

next one:

INPUT:
message1: a
message2: abcde
message3: abcdefg

MESSAGE 1a: a�� 
MESSAGE 2a: abcde 
MESSAGE 1ab: abcd 
MESSAGE 2ab: abcde 
MESSAGE 1b: abcd 
MESSAGE 2b: abcdefg 

.

    if (message1[0] == '\0')
    {
        memcpy(message1, echoBuffer, sizeof echoBuffer);
        fprintf(stderr, "MESSAGE 1: %s \n", message1);
    }
    else if (message1[0] != '\0' && message2[0] == '\0')
    {
        memcpy(message2, echoBuffer, sizeof echoBuffer);
        fprintf(stderr, "MESSAGE 2: %s \n", message2);
    }
    else if (message1[0] != '\0' && message2[0] != '\0')
    {
        fprintf(stderr, "MESSAGE 1a: %s \n", message1);
        fprintf(stderr, "MESSAGE 2a: %s \n", message2);
        memcpy(message1, message2, sizeof message2);
        fprintf(stderr, "MESSAGE 1ab: %s \n", message1);
        fprintf(stderr, "MESSAGE 2ab: %s \n", message2);
        memcpy(message2, echoBuffer, sizeof echoBuffer);
        fprintf(stderr, "MESSAGE 1b: %s \n", message1);
        fprintf(stderr, "MESSAGE 2b: %s \n", message2);
    }
}

Does anybody know what is wrong? This problem has been plaguing me.

I think the messages and echoBuffer are all 100 characters in size.

Answer 1

Is there a particular reason for using memcpy? I believe that strcpy(char* dest, char* source) would be easier to use. Maybe it could fix your problem

You must include string.h in order to use it