Thread: Any Memory Leak Here

  1. #1
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    Any Memory Leak Here

    Dear All,

    There is a part of a C code, that gives me ,apparently, a memory leak.
    I cannot find the exact place, and make sure if anything is wrong.
    I just wanted to see if anybody can help on this:


    Here is where the potential problem maybe:
    Code:
    void* my_function(void* ptr){
    	
           //this is taking a string, and parses its portions to separate argv, argc to pass to my_main()
    	MyStructure *main_input;
    	char *input_command_line = (char *)ptr;
    	main_input = (MyStructure *)malloc(sizeof(MyStructure));
    	main_input->argv = (char **)malloc(sizeof(char *));
    	parse_command_line(input_command_line, main_input);
    
    	my_main(main_input->argc,main_input->argv);
    
    	free(input_command_line);
    	free(main_input);
    
    	return;
    }
    Where MyStructure is defined like this:
    Code:
    typedef struct MyStructure{
        int argc;
        char** argv;
    
    } MyStructure;
    and the functions my_main(), and parse_command_line() are defined in the same c file like this:
    Code:
    void parse_command_line(char *command_line, MyStructure *return_value){
    	
    	return_value->argc = 0;
    	
    	return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    	
    	return_value->argv[return_value->argc] = strtok (command_line," ");
    	
    	while(return_value->argv[return_value->argc] != NULL){
    	    
    		(return_value->argc)++;
    		return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    		return_value->argv[return_value->argc] = strtok (NULL," ");
    		
    	}
    	return;
    }
    and:
    Code:
    int my_main(int argc, char **argv){
        /*Some stuff.....Nothing wrong here for sure*/
    
    return 0;
    }
    Last edited by akm3; 03-14-2009 at 04:00 PM.

  2. #2
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    You never free the allocation here:
    Code:
    return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    In fact, you even overwrite the allocated memory address. So you lose this address - so you can never freeit.
    Read the strtok manual...

  3. #3
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    Quote Originally Posted by EVOEx View Post
    You never free the allocation here:
    Code:
    return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    In fact, you even overwrite the allocated memory address. So you lose this address - so you can never freeit.
    Read the strtok manual...
    Well,

    I can free the memory at the end of "my_function()", but I don't know why the allocated memory is overwritten?

    I saw some examples of strtok(), they do not do memory allocation for the objects that strtok() returns, but in my case, if I don't do this, I still have the memory leak problem

    Is there any alternative solution to parse the string without having this allocation problems?

  4. #4
    Hurry Slowly vart's Avatar
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    but I don't know why the allocated memory is overwritten?
    not the memory, just the address -
    Code:
    return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    		return_value->argv[return_value->argc] = strtok (NULL," ");
    first line stores in your var address returned by malloc
    second line stores address returned by strtok effectively leaking the previous address
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

  5. #5
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    Quote Originally Posted by akm3 View Post
    Well,

    I can free the memory at the end of "my_function()", but I don't know why the allocated memory is overwritten?

    I saw some examples of strtok(), they do not do memory allocation for the objects that strtok() returns, but in my case, if I don't do this, I still have the memory leak problem

    Is there any alternative solution to parse the string without having this allocation problems?
    Well,

    Thanks for the reply.
    I converted the big file, I am working with to a small example.
    I tried many changes on that, but I still have the memory leak problem

    Here is my simple code:
    Code:
    #include <stdlib.h>
    #include <string.h>
    #include <stdio.h>
    
    typedef struct MyStructure{
        int argc;
        char** argv;
    
    } MyStructure;
    
    
    int my_main(int argc, char **argv)
    {
            int i;
    	printf("my_main is here\n");
    	for(i = 0; i < argc ; i++){
    		printf("In my_main: argv[%d]=%s\n",i,argv[i]);
    	}
    	return 1;
    }
    
    
    void parse_command_line(char *command_line, MyStructure *return_value){
    	
    	return_value->argc = 0;
    	
    	//return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    	
    	return_value->argv[return_value->argc] = strtok (command_line," ");
    	
    	while(return_value->argv[return_value->argc] != NULL){
    	    
    		(return_value->argc)++;
    		//return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    		return_value->argv[return_value->argc] = strtok (NULL," ");
    		
    	}
    	return;
    
    }
    
    void* av_function(void* ptr){
    	
    	MyStructure *main_input;
    	char *input_command_line = (char *)ptr;
    	main_input = (MyStructure *)malloc(sizeof(MyStructure));
    	main_input->argv = (char **)malloc(sizeof(char *));
    	parse_command_line(input_command_line, main_input);
    	printf("av_encode_decode called\n");
    	my_main(main_input->argc,main_input->argv);
    	printf("av_function called exited\n");
    	free(input_command_line);
    	free(main_input);
    
    	return;
    }
    int main()
    {
    	av_function("av -i testvideo.flv out.mog");
    	return 1;
    }
    I have commented out the allocations form the strings that are returned by strtok()
    But when I compile it in Cygwin(gcc -c myfile.c) I have the following complaiunt:

    8 [main] memtest 5976 _cygtls::handle_exceptions: Error while dumping state (probably corrupted stack)
    Segmentation fault (core dumped)
    Last edited by akm3; 03-15-2009 at 03:12 PM.

  6. #6
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    this code simply takes a string like "av -i testvideo.flv out.mog" in the av_function, and parses its words, and puts in MyStructure, then prints the values of argv[i]

    Is it a memory leak at all? And if so, how should I correct the code to get rid of the leak?
    Last edited by akm3; 03-15-2009 at 03:14 PM. Reason: Redundant

  7. #7
    Hurry Slowly vart's Avatar
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    your argv is array of 1 pointer, you are assigning a lot more members
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

  8. #8
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    Quote Originally Posted by vart View Post
    your argv is array of 1 pointer, you are assigning a lot more members
    Even this doesn't solve the issue:

    Code:
    #include <stdlib.h>
    #include <string.h>
    #include <stdio.h>
    
    typedef struct MyStructure{
        int argc;
        char** argv;
    
    } MyStructure;
    
    
    int my_main(int argc, char **argv)
    {
            int i;
    	printf("my_main is here\n");
    	for(i = 0; i < argc ; i++){
    		printf("In my_main: argv[%d]=%s\n",i,argv[i]);
    	}
    	return 1;
    }
    
    
    void parse_command_line(char *command_line, MyStructure *return_value){
    	
    	return_value->argc = 0;
    	
    	//return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    	
    	return_value->argv[return_value->argc] = strtok (command_line," ");
    	
    	while(return_value->argv[return_value->argc] != NULL){
    	    
    		(return_value->argc)++;
    		//return_value->argv[return_value->argc]=(char *)malloc(sizeof(char)*64);
    		return_value->argv[return_value->argc] = strtok (NULL," ");
    		
    	}
    	return;
    
    }
    
    void* av_function(void* ptr){
    	
    	MyStructure *main_input;
    	char *input_command_line = (char *)ptr;
    	main_input = (MyStructure *)malloc(sizeof(MyStructure));
    	main_input->argv = (char **)malloc(sizeof(char *)*256);
    	parse_command_line(input_command_line, main_input);
    	printf("av_encode_decode called\n");
    	my_main(main_input->argc,main_input->argv);
    	printf("av_function called exited\n");
    	free(input_command_line);
    	free(main_input);
    
    	return;
    }
    int main()
    {
    	av_function("av -i testvideo.flv out.mog");
    	return 1;
    }
    I see the problem is inside the function "parse_command_line()"
    Cygwin gives me a "sementation fault", and MSVC++ reports access violation.
    And I see its breaking inside that function, but I can't find out why, and cannot correct the issue there

  9. #9
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    Code:
    "av -i testvideo.flv out.mog"
    That's a string constant. So, you can't change it. Still, you pass it as a non-const string, and you modify it, which causes the access violation.

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