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GDB Not Showing Variable value

This is a discussion on GDB Not Showing Variable value within the Linux Programming forums, part of the Platform Specific Boards category; Hi All I wrote a small sample program for testing GDB in linux. The code is: Code: #include<stdio.h> void fun() ...

  1. #1
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    GDB Not Showing Variable value

    Hi All

    I wrote a small sample program for testing GDB in linux.

    The code is:

    Code:
    #include<stdio.h>
    
    void fun()
    {
     int x=20;
    
     printf("\n Inside Fun");
    }
    int main()
    {
    
     int x=10; 
     
     printf("\n In main \n");
     fun();  // Put Break point here
    
    }
    I put break point at fun() and try to print out value of x using:
    print x
    But it give me error that:
    No symbol "x" in current context.
    Can any body help me in this. I am using Ubuntu.

    Thanks

  2. #2
    - - - - - - - - oogabooga's Avatar
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    After setting the breakpoint, you have to start the program running so it can run up to that point. The command is "run args" where args is optional and represents the args you'd pass on the command line, if any.
    The cost of software maintenance increases with the square of the programmer's creativity. - Robert D. Bliss

  3. #3
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    Soory that I didn't mention that it is coming after running the program.
    It print successfully print:
    In main
    But after wards not the value of x.

    Thanks

  4. #4
    - - - - - - - - oogabooga's Avatar
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    Did you compile it with the -g option (to include debugging information) ?
    gcc -Wall -Wextra -g yourprog.c
    The cost of software maintenance increases with the square of the programmer's creativity. - Robert D. Bliss

  5. #5
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    Oh Thanks.. It's working now.

  6. #6
    Registered User ledow's Avatar
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    Also, what can sometimes happen, is that the compiler notices that x is not used and just optimises it away. This is quite common in debugging gcc programs, especially if you compiled with the -O switches and have code like that.

    When debugging in a debugger, include debug statements (-g) and turn off all optimisations (-O0).
    oogabooga likes this.

    - Compiler warnings are like "Bridge Out Ahead" warnings. DON'T just ignore them.
    - A compiler error is something SO stupid that the compiler genuinely can't carry on with its job. A compiler warning is the compiler saying "Well, that's bloody stupid but if you WANT to ignore me..." and carrying on.
    - The best debugging tool in the world is a bunch of printf()'s for everything important around the bits you think might be wrong.

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