double free or corruption (out)

This is a discussion on double free or corruption (out) within the C Programming forums, part of the General Programming Boards category; Hey guys I got an assignment due tomorrow of multiplying two matrices. I got everything done but when I free ...

  1. #1
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    double free or corruption (out)

    Hey guys I got an assignment due tomorrow of multiplying two matrices. I got everything done but when I free the second matrix then I get this error:

    Code:
    *** glibc detected *** ./a.out: double free or corruption (out): 0x0000000001f5e2f0 ***
    ======= Backtrace: =========
    /lib/libc.so.6[0x7fa69d033a58]
    /lib/libc.so.6(cfree+0x76)[0x7fa69d0360a6]
    ./a.out[0x400aad]
    /lib/libc.so.6(__libc_start_main+0xe6)[0x7fa69cfd8466]
    ./a.out[0x400659]
    ======= Memory map: ========
    00400000-00401000 r-xp 00000000 08:05 3498047                            /home/craig/Desktop/Cis308/a.out
    00601000-00602000 r--p 00001000 08:05 3498047                            /home/craig/Desktop/Cis308/a.out
    00602000-00603000 rw-p 00002000 08:05 3498047                            /home/craig/Desktop/Cis308/a.out
    01f5e000-01f7f000 rw-p 01f5e000 00:00 0                                  [heap]
    7fa698000000-7fa698021000 rw-p 7fa698000000 00:00 0 
    7fa698021000-7fa69c000000 ---p 7fa698021000 00:00 0 
    7fa69cda2000-7fa69cdb8000 r-xp 00000000 08:05 647270                     /lib/libgcc_s.so.1
    7fa69cdb8000-7fa69cfb8000 ---p 00016000 08:05 647270                     /lib/libgcc_s.so.1
    7fa69cfb8000-7fa69cfb9000 r--p 00016000 08:05 647270                     /lib/libgcc_s.so.1
    7fa69cfb9000-7fa69cfba000 rw-p 00017000 08:05 647270                     /lib/libgcc_s.so.1
    7fa69cfba000-7fa69d123000 r-xp 00000000 08:05 647470                     /lib/libc-2.8.90.so
    7fa69d123000-7fa69d322000 ---p 00169000 08:05 647470                     /lib/libc-2.8.90.so
    7fa69d322000-7fa69d326000 r--p 00168000 08:05 647470                     /lib/libc-2.8.90.so
    7fa69d326000-7fa69d327000 rw-p 0016c000 08:05 647470                     /lib/libc-2.8.90.so
    7fa69d327000-7fa69d32c000 rw-p 7fa69d327000 00:00 0 
    7fa69d32c000-7fa69d34b000 r-xp 00000000 08:05 647467                     /lib/ld-2.8.90.so
    7fa69d533000-7fa69d535000 rw-p 7fa69d533000 00:00 0 
    7fa69d545000-7fa69d54a000 rw-p 7fa69d545000 00:00 0 
    7fa69d54a000-7fa69d54b000 r--p 0001e000 08:05 647467                     /lib/ld-2.8.90.so
    7fa69d54b000-7fa69d54c000 rw-p 0001f000 08:05 647467                     /lib/ld-2.8.90.so
    7fffa5537000-7fffa554c000 rw-p 7ffffffea000 00:00 0                      [stack]
    7fffa55ff000-7fffa5600000 r-xp 7fffa55ff000 00:00 0                      [vdso]
    ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
    Aborted
    Here is my code:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    #define Mult(x, y) (x)*(y)
    
    
    typedef struct matrix
    {
    	int r;
    	int c;
    	int **mtx;
    }matrix;
    
    matrix m1;
    matrix m2;
    void MultiplyMatrices();
    
    int main(int argc,char * argv[])
    {
    	FILE *input = fopen(argv[1], "r");
    	if (input==NULL)
    	{
    		printf("Error Opening File.\n");
    		return 0;
    	}
    	int rows;
    	int cols;
    	fscanf(input, "%d %d" , &rows, &cols);
    	
    	//read in matrix 1
    	m1.r = rows;
    	m1.c = cols;
    	m1.mtx= malloc(m1.r*sizeof(int));
    	int i;
    	for(i=0; i<m1.r; i++)
    	{
    		m1.mtx[i] = malloc(m1.c*sizeof(int));
    	}
    	int j;
    	for(i=0; i<m1.r; i++)
    	{
    		for(j=0; j<m1.c; j++)
    		{
    			fscanf(input, "%d " , m1.mtx[i]+j);
    		}
    	}
    	//print matrix 1
    	printf("The first matrix is: \n");
    	for(i=0; i<m1.r; i++)
    	{
    		for(j=0; j<m1.c; j++)
    		{
    			printf("	%d ", m1.mtx[i][j]);
    		}
    		printf("\n");
    	}
    
    	//read in matrix 2
    	fscanf(input, "%d %d" , &rows, &cols);
    	m2.r = rows;
    	m2.c = cols;
    	m2.mtx= malloc(m2.r*sizeof(int));
    	for(i=0; i<m2.r; i++)
    	{
    		m2.mtx[i] = malloc(m2.c*sizeof(int));
    	}
    	for(i=0; i<m2.r; i++)
    	{
    		for(j=0; j<m2.c; j++)
    		{
    			fscanf(input, "%d " , m2.mtx[i]+j);
    		}
    	}
    	//print matrix 2
    	printf("The second matrix is: \n");
    	for(i=0; i<m2.r; i++)
    	{
    		for(j=0; j<m2.c; j++)
    		{
    			printf("	%d ", m2.mtx[i][j]);
    		}
    		printf("\n");
    	}
    
    	MultiplyMatrices();
    
    
    	//free memory
    	for(i=0;i<m1.r;i++)
    	{
    		free(m1.mtx[i]);
    	}
    	free(m1.mtx);
    	//I think these should be here, but it says I double deleted them.
    	for(i=0; i<m2.r;i++)
    	{
    		free(m2.mtx[i]);
    	}
    	free(m2.mtx);
    	fclose(input);
    }
    ^^ the two bold and underlined lines are the ones that cause the error.

    I took out MultiplyMatrices function as it didn't change anything. Thanks for any help,

    Craig.

  2. #2
    spurious conceit MK27's Avatar
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    In this,
    Code:
    m1.mtx= malloc(m1.r*sizeof(int*));
    	int i;
    	for(i=0; i<m1.r; i++)
    	{
    		m1.mtx[i] = malloc(m1.c*sizeof(int));
    	}
    You intend to create an array of int pointers, such that mtx[i][0] is the first element of a row pointed to by mtx[i]. But you don't do that, you create an array of ints. I added the red asterisk to correct this. Since they could be the same size, it may be okay...

    But that is not your double free() error
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    If I comment out the matrix multiply, I get printed matrices without any seeming fuss or muss or complaints from libc. Perhaps it is in your MultiplyMatrices?

  4. #4
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    Weird, It gave me that error before I implemented the multiplication. I commented it out and even cut it out and I still get the error. I'm pretty new to c, I'm not real sure what to do. I swear I've looked over this code 1000 times and m1 and m2 are identical, but only m2 gives me the error.

    Thanks for the replies.

  5. #5
    CSharpener vart's Avatar
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    m1.mtx= malloc(m1.r*sizeof(int))ж

    should be sizeof (int*) or better

    sizeof *m1.mtx

    same for the second matrix
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

  6. #6
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    Thanks vart, that worked. I remember doing that in lab now that you mention it. I appreciate everyones help.

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