malloc / new operator

[mikalv]

I'm reading a tutorial from learncpp.com now, and I'm trying to create a variable(/pointer) with malloc/new, print it, and delete it.

#include <stdlib.h>
#include <stdio.h>

int main(int &argc, char **argv) {
    int *pnValue = (int*) malloc(7);
    *pnValue = 7;
    printf("Pointer adress: &#37;p\n", pnValue);
    free(pnValue);
}

but, I got this:

mikalv@mikalv-laptop:~/Projects/CExamples$ gcc testalloc.cpp -o kake
/tmp/ccm9ZMkq.o:(.eh_frame+0x11): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status

and I also tried this:

#include <stdlib.h>
#include <stdio.h>

int main(int &argc, char **argv) {
    int *pnValue = new int;
    *pnValue = 7;
    printf("Pointer adress: %p\n", pnValue);
    delete pnValue;
}

but this also fail, but with another message.

/tmp/cc0FszjM.o: In function `main':
dynamicallocation.cpp:(.text+0x19): undefined reference to `operator new(unsigned int)'
dynamicallocation.cpp:(.text+0x43): undefined reference to `operator delete(void*)'
/tmp/cc0FszjM.o:(.eh_frame+0x11): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status

Can someone tell me what I'm doing wrong? and why I get these messages, so I can learn to next time..

[MacGyver]

Offhand, I see three mistakes:

1. argc shouldn't be declared as being a reference, but just a straight int.... ie. int argc.
2. malloc() needs an argument as to how many bytes to allocate. While it's a possibiliy an int may be seven bytes in size, that is unlikely. Allocate sizeof(int) or perhaps more preferably, sizeof(*pnValue).
3. You should be using the C++ header file equivalents of the C header files: ie. cstdio instead of stdio.h and cstdlib instead of stdlib.h.

[laserlight]

They both look like they should (or at least could) work, though the first one is weird because you allocate 7 bytes for an int, but an int is more likely 4 or 8 bytes. Also, note that main's first argument is usually passed by value, not by reference.

I suggest that you try:

#include <stdlib.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
    int* pnValue = (int*)malloc(sizeof *pnValue);
    *pnValue = 7;
    printf("Pointer adress: &#37;p\n", (void*)pnValue);
    free(pnValue);
}

or for a more C++ish approach:

#include <iostream>

int main(int argc, char* argv[]) {
    int* pnValue = new int;
    *pnValue = 7;
    std::cout << "Pointer adress: " << pnValue << '\n';
    delete pnValue;
}

[CornedBee]

These errors mean that you're not linking against the C++ runtime. Compile with g++, not gcc.