String Vector Class -> data persists on heap memory?

Hello,

I use this following function (on a microcontroller) to split a string into parts by using a delemiter.

E.g.:

Code:

---

std::vector<std::string> parts = splitStringToVectorArray("String1;String2;String3", ";");

---

The function works, but every time I call the function, data keeps persist on the heap memory. So I will run out of memory at all.

I read that this problem could belong to the push_back command.
So my question, is there any command missing in the function to release the used heap memory, or is something else wrong?

Code:

---

std::vector<std::string> splitStringToVectorArray(const std::string &inputString, const std::string &delimiter) 
    {

        std::vector<std::string> vectorArray;
        if (inputString.empty() || delimiter.empty())
        {
            vectorArray.push_back(inputString);
            return vectorArray;
        }
        size_t initiation = 0;
        size_t position;
        while ((position = inputString.find(delimiter, initiation)) != std::string::npos)
        {
            std::string stringValue = inputString.substr(initiation, position - initiation);
            if (!stringValue.empty())
            {
                vectorArray.push_back(stringValue);
            }
            initiation = position + delimiter.length();
        }
        if (initiation < inputString.length())
        {
            vectorArray.push_back(inputString.substr(initiation));
        }

        return vectorArray;
    }

---

Thanks, Michael

How are you determining that you have a memory leak?

As written, it seems well behaved.

Code:

---

#include <iostream>
#include <string>
#include <vector>

std::vector<std::string> splitStringToVectorArray(const std::string &inputString, const std::string &delimiter) 
{

    std::vector<std::string> vectorArray;
    if (inputString.empty() || delimiter.empty())
    {
        vectorArray.push_back(inputString);
        return vectorArray;
    }
    size_t initiation = 0;
    size_t position;
    while ((position = inputString.find(delimiter, initiation)) != std::string::npos)
    {
        std::string stringValue = inputString.substr(initiation, position - initiation);
        if (!stringValue.empty())
        {
            vectorArray.push_back(stringValue);
        }
        initiation = position + delimiter.length();
    }
    if (initiation < inputString.length())
    {
        vectorArray.push_back(inputString.substr(initiation));
    }

    return vectorArray;
}
   
int main()
{
    std::vector<std::string> parts = splitStringToVectorArray("String1;String2;String3", ";");
    std::cout << parts[0] << std::endl;
}


$ g++ -g baz.cpp
$ valgrind ./a.out
==95652== Memcheck, a memory error detector
==95652== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==95652== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==95652== Command: ./a.out
==95652==
String1
==95652==
==95652== HEAP SUMMARY:
==95652==    in use at exit: 0 bytes in 0 blocks
==95652==  total heap usage: 6 allocs, 6 frees, 73,976 bytes allocated
==95652==
==95652== All heap blocks were freed -- no leaks are possible
==95652==
==95652== For lists of detected and suppressed errors, rerun with: -s
==95652== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

---

Thx for your work!

I use:

Code:

---

Serial.println("Free Heap: "+String(ESP.getFreeHeap()));

---

to get free Heap

I run the function as a method in class on a ESP32.


I found this article, may be a heap fragmentation problem?

Using the C++ Standard Template Library with Arduino | Chris Claxton's Blog

It could be.
Memory constrained systems are far more reliant on solid library implementations doing the right thing.

Is it easy/possible for you to try those alternative STL implementations?

Where are you getting inputString from?
What is the lifetime of the parts result?

If you have a much simpler function, do you see the same heap erosion?

Code:

---

std::vector<std::string> splitStringToVectorArray(const std::string &inputString, const std::string &delimiter) 
    {
        std::vector<std::string> vectorArray;
        vectorArray.push_back("test");
        return vectorArray;
    }

---

Hi Salem,

your second function behaves the same.
The input string comes from a global running task, so no user input string,

the output of the function goes to a LCD Class to be displayed on screen.
This LCD-Class needs a const char * as input, so I use the convert function vectorArrayToCharPointer.

Normally after the u8g2.drawUTF8 is done the pointer char will be deleted from heap by the u8g2.sendBuffer(); command.


Here a short test without using external inputs.

Code:

---

std::vector<std::string> splitStringToVectorArray(const std::string &inputString, const std::string &delimiter)
    {
        std::vector<std::string> vectorArray;
        vectorArray.push_back("test");
        return vectorArray;
    }

    const char *vectorArrayToCharPointer(std::string s)
    {

        char *pc = new char[s.size() + 1];
        strcpy(pc, s.c_str());
        return pc;
    }
   
   
      void displayInfoMultiline(String infoString, uint8_t fontUsed = 3)
    {



        std::vector<std::string> test2 = splitStringToVectorArray("asd;asd;asd", ";");
       

        ...
 
           
           
            u8g2.clearBuffer();
            u8g2.drawUTF8(0, ySpace, vectorArrayToCharPointer(test2[0]));
            u8g2.sendBuffer();
       
    }

---

Four calls result:

Free Heap: 340064
Free Heap: 340040
Free Heap: 340016
Free Heap: 339992


I coded a new Split function without vector, now it works.

Quote:

---

Originally Posted by MichaelMMs

Hi Salem,

your second function behaves the same.
The input string comes from a global running task, so no user input string,

the output of the function goes to a LCD Class to be displayed on screen.
This LCD-Class needs a const char * as input, so I use the convert function vectorArrayToCharPointer.

Normally after the u8g2.drawUTF8 is done the pointer char will be deleted from heap by the u8g2.sendBuffer(); command.


Here a short test without using external inputs.

Code:

---

std::vector<std::string> splitStringToVectorArray(const std::string &inputString, const std::string &delimiter)
    {
        std::vector<std::string> vectorArray;
        vectorArray.push_back("test");
        return vectorArray;
    }

    const char *vectorArrayToCharPointer(std::string s)
    {

        char *pc = new char[s.size() + 1];
        strcpy(pc, s.c_str());
        return pc;
    }
   
   
      void displayInfoMultiline(String infoString, uint8_t fontUsed = 3)
    {



        std::vector<std::string> test2 = splitStringToVectorArray("asd;asd;asd", ";");
       

        ...
 
           
           
            u8g2.clearBuffer();
            u8g2.drawUTF8(0, ySpace, vectorArrayToCharPointer(test2[0]));
            u8g2.sendBuffer();
       
    }

---

Four calls result:

Free Heap: 340064
Free Heap: 340040
Free Heap: 340016
Free Heap: 339992


I coded a new Split function without vector, now it works.

---

Your vectorArrayToCharPointer function is the memory leak. You don't need to allocate anything anyway. Just call test2[0].c_str() and you'll get a pointer to the bytes of the string.

hi Sir Galahad,

thanks, you are right.