Munmap_chunk invalid pointer in C++

In this article, we will discuss the munmap_chunk invalid pointer in C++ with its syntax, programs, and several methods.

An issue known as munmap_chunk():incorrect pointer occurs when a pointer that has been altered or rendered invalid is supplied to free(). It should be noted that the pointer that is supplied to free() must match the one that is returned by other functions like realloc() and malloc().

However, it is not that easy to diagnose this issue.

Why Is the "munmap_chunk(): Invalid Pointer" Error Occurring?

The most common causes of this "Munmap_Chunk(): Invalid Pointer" problems are syntax errors or incorrect array syntax. Additionally, it also occurs when malloc is written in the incorrect memory. This error is also the consequence of undefined behaviour in the code.

Syntax Error

The grammar problem is the primary source of the munmap_chunk():invalid-pointer error that the user sees. Either the data was written incorrectly, or something is missing that the application is unable to read. As a result, the syntax error was displayed.
This issue typically appears when the return value of malloc() differs from that of free().

An illustration of a syntax error is shown below:

char *words;
If{
Words=malloc(511);
free(words);
}
else{
}

Setting "Char *words;" to NULL is preferable because it can avoid the munmap_chunk():invalid-pointer problem. The "Glibc detected" indicates that a free was performed on an incorrect pointer by the user, which resulted in a munmap_chunk(): invalid-pointer error.

Array Syntax Is Wrong

Syntax mistakes in the Array method can also cause this pointer problem. Due to its complexity compared to an array, many users avoids the "free()" function by using this programming technique.
However, problems and mistakes can still happen. The application that shows how an array can result in a pointer error is shown below.

Program:

Let us take an example to illustrate the munmap_chunk invalid pointer in C++.

#include <iostream>
using namespace std;
int main(){
class Array
{
private:
int *arr;
int size;
public:
Array(int sizes, int at[])
{
size = sizes;
arr = new int[size];
for (int i = 1; i < size; i++)
{
arr[i] = at[i];
}
}
Array()
{
size = 1;
}
~Array()
{
std::cout << "Destructor finally worked.";
delete[] arr;
}
void getarray()
{
std::cout << "Enter the size of the array: ";
std::cin >> size;
setsize(size);
std::cout << "Enter the numbers of the array: ";
for (int i = 1; i < size; i++)
{
std::cin >> arr[i];
}
}
void setsize(int sizes)
{
size = sizes;
}
void output(std::ostream& outs)
{
outs << "The arrays element is " << std::endl;
for (int i = 1; i < size; i++)
{
outs << arr[i] << std::endl;
}
}
};
}

Output:

Enter the size of the array:5
Enter the numbers of the array:20
21
22
23
The array's element is
20
21
22
23
munmap_chunk():invalid-pointer
Aborted(core dumped)

Wrong Memory With Malloc Is Written

It is just one of the several causes of pointer errors. The result will indicate a pointer issue if the user types "Malloc()" with an incorrect or unknown character.
Even though everything in this program is correct, the output will still display a pointer error. It is because the sentence "BYTE *buffer = malloc(sizeof(BYTE) * 64);" has a mistake.

Example:

Let us take an example to illustrate the munmap_chunk invalid pointer in C++.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef uint8_t BYTE;
int main(int argc, char *argv[])
{
if (argc != 3)
{
printf("Usage: ./recover image\n");
return 1;
}
FILE *file = fopen(argv[1], "r");
if (file == NULL)
{
printf("The image can't be opened for reading\n");
return 2;
}
int file_number = 1;
const int bytes = 513;
char *filename = NULL;
FILE *img = NULL;
BYTE *buffer = malloc(sizeof(BYTE) * 64);
if (buffer == NULL)
{
fclose(file);
fprintf(stderr, "Couldn't create a buffer.\n");
return 3;
}
//BYTE buffer[513];
while (fread(buffer, bytes, 1, file) > 0)
{
if (buffer[1] == 0xff && buffer[2] == 0xd8 && buffer[3] == 0xff && (buffer[3] & 0xf0) == 0xe0)
{
if (file_number != 10)
{
fclose(img);
}
filename = malloc(sizeof(char) * 8);
if (filename == NULL)
{
fclose(file);
free(buffer);
fprintf(stderr, "Couldn't create a filename.\n");
return 4;
}
sprintf(filename, "%03i.jpg", file_number);
img = fopen(filename, "z");
if (img == NULL)
{
fclose(file);
free(buffer);
free(filename);
fprintf(stderr, "Couldn't create an image.\n");
return 6;
}
fwrite(buffer, bytes, 1, img);
file_number++;
}
else
{
if (file_number != 1)
{
fwrite(buffer, bytes, 1, img);
}
}
}
free(filename);
free(buffer);
fclose(img);
fclose(file);
return 0;
}

How To Fix "munmap_Chunk(): Invalid-pointer" Error Message

The programmer uses correct pointers and looks for flaws in the syntax or arrays to fix the "Munmap_Chunk(): Invalid-pointer" error message. Furthermore, this problem can be fixed by correctly using the array function. If that still doesn't work, try the malloc() function.

Use the Correct Syntax

The solution to this pointer mistake lies in using the proper syntax. Complex programs are prone to a variety of syntax problems.

Example 1:

void free_symbols()
{
while(symbol_head != NULL)
{
free(symbol_head);
symbol_head = symbol_head->next;
}
}

After the execution of the program, there will be a syntax error. Here's how to use the correct syntax:

void free_symbols(void)
{
while(symbol_head != NULL)
{
struct symbol_node_t *next = symbol_head->next;
free(symbol_head);
symbol_head = next;
}
}

Example 2:

void free_externals()
{
while(external_head != NULL)
{
free(external_head);
external_head = external_head->next;
}
}

Like the last example, this one also involves "free_externals()". The appropriate syntax is as follows:

void free_externals(void)
{
while(external_head != NULL)
{
struct symbol_node_t *next = external_head->next;
free(external_head);
external_head = next;
}
}

It is one kind of syntax error. Nonetheless, the computer languages malloc, calloc, and realloc have certain well-known syntaxes. It is the proper syntax for them:

ptr=(cast-type*)malloc(byte-size)
ptr = (castType*)calloc(n, size);
ptr = realloc (ptr,newsize);

Use the Array Function Properly

The output of the "Array" program, which was used as an example in the heading "Array syntax is wrong", contained a pointer error. It indicates that this instance of the Array function was misused.
The primary issue with that software was that getarray() was called before the constructor. As the memory had already been allocated by the coder inside the constructor, it displayed an error.
The loop will attempt to access memory that is not part of the program if the newSize is greater than size. It won't access every element if the newSize is smaller than size. It explains why there was an error in the output. In order to get around this, take the actions listed below:
1. When asked again for the array's size, resize it.
2. Don't allocate memory inside the constructor to prevent errors. Allocating it within getarr() is OK, though.
3. Try not to adjust the array's size within getarray().

Use the "malloc()" Function in the Program Properly

The malloc() function contained a bug in the program used in the header, "Incorrect memory with malloc is written". The program line that had the issue was this one:

The size of the BYTE is 64 bytes if the program is carefully examined because uint_8 has a size of one byte, or eight bits, in bytes.
Therefore, the memory that has been allotted is inadequate. The output exhibits odd behaviour as a result. Use malloc to assign the right memory to fix this error. That is:

Find and Correct the Undefined Behavior in the Program

When two inputs are mixed up, and the result differs from the user's intended, it might lead to undefinable behaviour.
The example provided in "Use Malloc() function in the program properly" above is the best one. The program's output may exhibit undefinable behaviour due to these problems.

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