strcat in windows crashes program

This is a discussion on strcat in windows crashes program within the Windows Programming forums, part of the Platform Specific Boards category; Code: #include <windows.h> #include <string.h> char * one = "hello "; char * two = "world"; int WINAPI WinMain(HINSTANCE, HINSTANCE, ...

  1. #1
    Registered User Diamonds's Avatar
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    Question strcat in windows crashes program

    Code:
    #include <windows.h>
    #include <string.h>
    
    char * one = "hello ";
    char * two = "world";
    
    int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int) 
    {
    	MessageBox(NULL, strcat(one,two), "Sample", MB_OK);
    	return 0; 
    }
    This will compile but crash when it's run. Why?

  2. #2
    train spotter
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    because there is not enough space in the string 'one' to hold both words.
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  3. #3
    Registered User Diamonds's Avatar
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    o, danit
    Last edited by Diamonds; 12-04-2002 at 01:37 AM.

  4. #4
    Registered User Diamonds's Avatar
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    wait, what does it return then? a pointer to string 1 ?

  5. #5
    Registered User Diamonds's Avatar
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    did a search, found the answer

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    Banned master5001's Avatar
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    Not that I would ever defend windows. But why blame windows for code that shouldn't work on any OS?

  7. #7
    Confused Magos's Avatar
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    Can you really modify those strings? Aren't they constant?

    Wouldn't you need to do this at least?:

    char one[64] = "Hello";
    MagosX.com

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  8. #8
    Registered User Penguin of Oz's Avatar
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    Also, some people may argue it's nicer to use sprintf(...);:

    Code:
    char one[64] = { "hello " };
    char two[6] = { "world" };
    
    sprintf(one, "%s%s", one, two);
    MessageBox(NULL, one, "Meep", MB_OK | MB_ICONINFORMATION);
    Just a thought.
    "I don't think there's anything else I can do... my shoes are tied"

  9. #9
    End Of Line Hammer's Avatar
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    >>some people may argue it's nicer to use sprintf(...);
    strncat() would be a better choice, imho.

    >>sprintf(one, "%s%s", one, two);
    Here you are using "one" as both a target and a source pointer, I'm going to guess that is undefined behaviour.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  10. #10
    Registered User Penguin of Oz's Avatar
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    I had my doubts about that working, I appreciate it's messy, but Dev-C++/cygwin/mingw32 lapped it up nicely.

    Personally, I usually keep a char szMessage[256]; or something in any functions that need to use message boxes with variables in.
    "I don't think there's anything else I can do... my shoes are tied"

  11. #11
    Registered User johnnie2's Avatar
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    If you really wanted to force that to work, a plausible way would be:

    Code:
    char *one = new char[65];
    memset(one, 0, 65);
    memcpy(one, "hello", 5);
    
    char *two = new char[6];
    memset(two, 0, 6);
    memcpy(two, "world", 5);
    
    sprintf(one + strlen(one), "%s", two);
    MessageBox(NULL, one, "Meep", MB_OK | MB_ICONINFORMATION);
    Which would produce "helloworld".
    Last edited by johnnie2; 12-04-2002 at 09:17 PM.
    "Optimal decisions, once made, do not need to be changed." - Robert Sedgewick, Algorithms in C

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    Quote
    Code:
    #include <windows.h>
    #include <string.h>
    
    char * one = "hello ";
    char * two = "world";
    
    int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int) 
    {
    	MessageBox(NULL, strcat(one,two), "Sample", MB_OK);
    	return 0; 
    }
    Here's how to do it (IMHO)
    Code:
    #include <windows.h>
    #include <string.h>
    
    char  one[30] = "hello ";
    char * two = "world";
    
    int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int) 
    {
            strcat(one, two);
    	MessageBox(NULL, one, "Sample", MB_OK);
    	return 0; 
    }

  13. #13
    End Of Line Hammer's Avatar
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    strncat() is much safer than strcat() and sprintf() for this, you should protect your buffers
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  14. #14
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    strncat() should be used when you can't guarantee that the concatonated string will fit in your destination buffer. In this case we have complete control over the length of the strings and the size of the destination buffer, therefore no need for strncat(). Another use for strncat() would be if you want to copy only a certain number of chars or if the source string doesn't have a terminating null.

    -Futura

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