CODEWITHSUNDEEP
cmemorysegmentation-faultmallocfree
Tom Doodler
Tom Doodler

Reputation: 1559

free crashing with signal SIGTRAP

Im writing a small console based application for the windows command line.

Im allocating memory for two arrays, chi and chi_comp like this:

/* allocating memory for chi */
if ((chi = (int *)malloc(cm * sizeof(int))) == NULL)
{
    printf("Error allocating %i bytes of memory.\n", lm * sizeof(int));
    return CMD_NONE;
}

/* allocating memory for chi_comp */
if ((chi_comp = (int *)malloc(cm * sizeof(int))) == NULL)
{
    printf("Error allocating %i bytes of memory.\n", cm * sizeof(int));
    return CMD_NONE;
}

A bit later in the code I initialize them

for (i = 0; i < cm; i++)
{
    chi[i] = -1;
    chi_comp[i] = -1;
}

and use them like

chi[grade] = i;
chi_comp[i] = grade;

and 

if (chi_comp[i] != -1)
{
    printf(" %i ", v[chi_comp[i]][0]);
}

Working with them works fine but when I try to free the memory when I don't need it no more the program crashes.

free(chi);
free(chi_comp);

Debugging with gdb results the following:

warning: HEAP[m.exe]: warning: Heap block at 003518B8 modified at 003518CC past requested size of c

Program received signal SIGTRAP, Trace/breakpoint trap. 0x776f0b2d in ntdll!RtlpNtEnumerateSubKey () from C:\Windows\system32\ntdll.dll

chi in this case values 003518C0 and chi_comp values 003518E8

Upvotes: 1

Views: 2697

Answers (2)

Sourav Ghosh
Sourav Ghosh

Reputation: 134376

Following the comments below the question,

it appears that, in your code, by saying

 chi[grade] = i;

you're going out of bounds. Accessing out of bound memory invokes undefined behavior.You should put a check like

 if (grade < cm)
       chi[grade] = i;

Upvotes: 2

gsamaras
gsamaras

Reputation: 73424

From the error message:

warning: HEAP[m.exe]: warning: Heap block at 003518B8 modified at 003518CC past requested size of c

I suspect you are going out of bounds somewhere in your code, so check your counters please. What tells me that is the past requested size of. Make sure you read twice the error messages, they are for your own good. :)

Next time you post, make sure you provide a minimal example of your bitte.

Upvotes: 2

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