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Something Loopy in Assigning Strings

Discussion in 'C' started by MattFunke, Sep 17, 2007.

  1. MattFunke

    MattFunke New Member

    I tried this in desperation after strcat() refused to work. I just want to concatenate three strings. Can anyone tell me why this doesn't work? I can see the creation of "10", but not of "11", though there's plenty of room on the disk for both. Moreover, if I ask for a printf of fieldn and strlen(fieldn) for all three fields, I get the right responses. field1[] is more than long enough to handle the job.

    Code:
    [COLOR=Red][FONT=Courier New]void AssembleData(char field1[], char field2[], char field3[])
    {
        int i;
        int startPos;
        int stopPos;
    
        if (field2[0] != '\0')
        {
            startPos = strlen(field1);
            stopPos = startPos + strlen(field2);
    
            system("touch /var/log/10\n");
    
            for (i = startPos; i < stopPos; i++)
            {
                field1[i] = field2[i - startPos];
            }
    
            system("touch /var/log/11\n");
    
            if (field3[0] != '\0')
            {
                startPos += strlen(field2);
                stopPos += strlen(field3);
    
                for (i = startPos; i < stopPos; i++)
                {
                    field1[i] = field2[i - startPos];
                }
            }
        }
    }[/FONT][/COLOR]
     
  2. DaWei

    DaWei New Member

    That's just silly. Disk operations are orders of magnitude slower than memory operations. Use strcat or strncat. They work. If you can't get them to work, show THAT code not this grossly over-footprint, underperforming stuff.
     
  3. MattFunke

    MattFunke New Member

    I explained in the first message that I tried strcat() and that it doesn't work, either. Here's the code. As usual, I can get "10" but not "11".

    Code:
    [COLOR=Red][FONT=Courier New]void AssembleData(char field1[], char field2[], char field3[])
    {
        system("touch /var/log/10\n");
    
        field1 = strcat(field1, field2);
        field1 = strcat(field1, field3);
    
        system("touch /var/log/11\n");
    }[/FONT][/COLOR]
    I would appreciate any help you could lend, but I would also appreciate it if you could acknowledge the things that I've already mentioned I've tried without success.
     
  4. MattFunke

    MattFunke New Member

    Found it! Here's the problem. This is what I was doing, essentially:

    Code:
    #define HI_THERE "hi "
    #define ID10T "idiot"
    char *data;
    
    data = strcat(HI_THERE, ID10T);
    ... and the statement, of course, after the preprocessor was done with it, looked like this:

    Code:
    data = strcat("hi ", "idiot");
    It was trying to concatenate literals, not string variables. This works:

    Code:
    char data[80] = HI_THERE;
    char data2[80] = ID10T;
    
    data = strcat(data, data2);
    <dope slaps self>
     
  5. DaWei

    DaWei New Member

    Actually, the second string can be a literal. There MUST be enough storage in the destination string to accomodate the original plus the second string (literal or otherwise).
     

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