I have a function which when compiled using gcc works fine, but when I compile it with g++, it gives me this error:
bon_io.cpp:In function ‘lruc_item* lruc_pop_or_create_item(lruc*)’:
bon_io.cpp:4751: error: invalid conversion from ‘void*’ to ‘lruc_item*’
Code:
typedef struct {
void *value;
void *key;
uint32_t value_length;
uint32_t key_length;
uint64_t access_count;
void *next;
} lruc_item;
lruc_item* lruc_pop_or_create_item(lruc *cache1)
{
lruc_item *item = NULL;
if(cache1->free_items) {
item = cache1->free_items;
cache1->free_items = item->next; [LINE 4751]
} else {
item = (lruc_item *) calloc(sizeof(lruc_item), 1);
}
return item;
}
I am trying to use this function with a c++ code, that's why need to compile it with g++, it works fine if I compile it using gcc but not with g++.
Can anyone please suggest me a way out to make this work with g++ ?
Thanks
How about:
cache1->free_items = (lruc_item *) item->next;
but then why is it that it gets compiled perfectly using gcc and gives
me error with g++
Because in C++ you can't automatically convert from void * to another pointer type.
Related
I accidentally removed a const qualifier from a derived class implementation of a virtual method. I usually use clang which issues a warning about that. When I switched to gcc with Wall the thing goes completely unnoticed. Why is that? Here is my file:
$ cat main.cpp
#include <iostream>
class Father {
public:
virtual int get() const { return 8; }
};
class Son : public Father {
public:
virtual int get() /* const */ { return 6; }
};
int main(int argc, char **argv)
{
Father *f = new Son;
std::cout << f->get() << "\n";
return 0;
}
And here are the compilation outputs for gcc and clang:
$ clang++ -Wall main.cpp -o main
main.cpp:10:14: warning: 'Son::get' hides overloaded virtual function
[-Woverloaded-virtual]
virtual int get() /* const */ { return 6; }
^
main.cpp:5:14: note: hidden overloaded virtual function 'Father::get' declared
here: different qualifiers ('const' vs unqualified)
virtual int get() const { return 8; }
^
1 warning generated.
And
$ g++ -Wall main.cpp -o main
$ ./main
8
My gcc version is 4.8.5
posix gcc version 4.8.5 20150623 (Red Hat 4.8.5-4) (GCC)
I have two cpp files：
1.cpp and 2.cpp
while there is a static function in 1.cpp called by 2.cpp。
In most machine，we should like this：
g++ 2.cpp 1.cpp
or it will cause compile error or runtime error。
However，in my machine with gcc 4.8.5，I must compile using “g++ 1.cpp 2.cpp” to make it run successful。
Is this the property of gcc4.8.5？ or there is something wrong on my soft，or I used it wrong？
==============================================================
My machine is centos7 installed on virtulbox of mac. Here is my code:
1.h
#include <map>
using namespace std;
class A {
private:
A();
static A _instance;
map<int, int> test_map;
public:
static A& get_instance();
static void fun();
};
1.cpp
#include <iostream>
#include "1.h"
using namespace std;
A A::_instance;
A::A() {
cout << "A::A()\n";
}
A& A::get_instance() {
cout << "A::get_instance()\n";
return A::_instance;
// static A instance;
// return instance;
}
void A::fun() {
cout << "A::fun()\n";
get_instance().test_map[1];
}
main.cpp
#include <iostream>
#include "1.h"
using namespace std;
int test() {
cout << "test()\n";
A::fun();
return 0;
}
int y = test();
int main() {
cout << "main()\n";
A::fun();
}
In most machine and in what I see in the web, we should compile like this:
g++ main.cpp 1.cpp
But in my machine, I must compile like this:
g++ 1.cpp main.cpp
what's wrong with my machine or my gcc?
I think you are facing the static initialization order fiasco which is a classical C++ bug. If initialization function test() in main.cpp is called before constructor for A::_instance has been called, your code will access uninitialized A::_instance::test_map field which is likely to cause segmentation fault. I suggest you rewrite getInstance to create instance when needed:
A *A::_instance;
A& A::get_instance() {
cout << "A::get_instance()\n";
if(!_instance)
_instance = new A;
return *A::_instance;
}
As a side note, I suggest you to use AddressSanitizer to autodetect this and similar types of errors.
Supposedly Arduino's IDE > 1.6.2 has C++11 support.
I have just freshly downloaded and run version 1.6.9 on OSX (and as others have reported, this repros on Windows as well, with 1.6.9/1.6.10).
I cannot get this simple program to compile:
constexpr int get_five() { return 5; }
void setup() {
Serial.begin(9600);
Serial.println(get_five());
}
void loop() {
}
I receive this error when I try to build or upload:
sketch_jul25a:1: error: 'constexprint' does not name a type
constexpr int get_five() { return 5; }
^
exit status 1
'constexprint' does not name a type
I've looked at this question and answer, but it is supposedly no longer applicable in 1.6.9 version of the IDE that I am using - error: 'constexpr' does not name a type m- arduino ide
I have dug into the temporary files that are output by the IDE when building, and it seems it is trying to automatically generate headers for functions (I assume for multi-file sketch support), and does the wrong thing when it encounters constexpr:
#include <Arduino.h>
#line 1 "/Users/<my_username>/Documents/Arduino/sketch_jul25a/sketch_jul25a.ino"
#line 1 "/Users/<my_username>/Documents/Arduino/sketch_jul25a/sketch_jul25a.ino"
#line 1 "/Users/<my_username>/Documents/Arduino/sketch_jul25a/sketch_jul25a.ino"
constexprint get_five(); // **** <- This looks to be the culprit
#line 3 "/Users/<my_username>/Documents/Arduino/sketch_jul25a/sketch_jul25a.ino"
void setup();
#line 9 "/Users/<my_username>/Documents/Arduino/sketch_jul25a/sketch_jul25a.ino"
void loop();
#line 1 "/Users/<my_username>/Documents/Arduino/sketch_jul25a/sketch_jul25a.ino"
constexpr int get_five() { return 5; }
void setup() {
Serial.begin(9600);
Serial.println(get_five());
}
void loop() {
}
Is this a bug in the Arduino IDE? Is it unique to OSX? Is there a workaround that allows constexpr to work?
In googling I have found that some Arduino libraries are using constexpr, so I am assuming it could be made to work in some cases.
This is a known limitation of the arduino-builder.
Until it is fixed, you can add a prototype yourself above the function. This will prevent the IDE from incorrectly generating its own.
constexpr int get_five();
constexpr int get_five() { return 5; }
void setup() {
Serial.begin(9600);
Serial.println(get_five());
}
void loop() {
}
I'm using gcc-4.7.1 on windows 8 Release Preview with git-bash.
$ g++ -v
Using built-in specs.
COLLECT_GCC=c:\Users\nikhil bhardwaj\mingw64\bin\g++.exe
COLLECT_LTO_WRAPPER=c:/users/nikhil bhardwaj/mingw64/bin/../libexec/gcc/x86_64-w
64-mingw32/4.7.1/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: /home/drangon/work/mingw-w64-dgn/source/gcc/configure --host=x8
6_64-w64-mingw32 --target=x86_64-w64-mingw32 --disable-nls --enable-languages=c,
c++,objc,obj-c++ --with-gmp=/home/drangon/work/mingw-w64-dgn/build/for_target --
enable-twoprocess --disable-libstdcxx-pch --disable-win32-registry --prefix=/hom
e/drangon/work/mingw-w64-dgn/target --with-sysroot=/home/drangon/work/mingw-w64-
dgn/target
Thread model: win32
gcc version 4.7.1 20120524 (prerelease) (GCC)
When I try to compile a small code snippet,
using namespace std;
struct node
{
int data;
node *left, *right;
};
node *newNode(int data)
{
node *node = new (struct node);
node->data = data;
node->left = nullptr;
node->right = NULL;
return node;
}
I get this error,
$ g++ -I../includes bst.cpp
bst.cpp: In function 'node* newNode(int)':
bst.cpp:13:18: error: 'nullptr' was not declared in this sc
bst.cpp:14:19: error: 'NULL' was not declared in this scope
I'm not able to use either NULL or nullptr, do I need to include some header files?
Try in c++11 mode:
g++ -std=c++11 -I../includes bst.cpp
I am using LD_PRELOAD to hook a library function, and in Linux it works perfectly. But I cannot figure out how to do the equivalent in OSX.
The setup I have on Linux is as follows:
The code is:
#include <stdio.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <unistd.h>
#include <ruby.h>
void
rb_raise(unsigned long exc, const char *fmt, ...)
{
static void (*libruby_rb_raise)
(unsigned long exc, const char *fmt, ...) = NULL;
void * handle;
char * error;
if (!libruby_rb_raise) {
handle = dlopen("/path/to/libruby.so",
RTLD_LAZY);
if (!handle) {
fputs(dlerror(), stderr);
exit(1);
}
libruby_rb_raise = dlsym(handle, "rb_raise");
if ((error = dlerror()) != NULL) {
fprintf(stderr, "%s\n", error);
exit(1);
}
}
// ...code...
return Qnil;
}
Which I then compile with:
gcc -Wall -O2 -fpic -shared -ldl -g -I/path/to/includes/ -o raise_shim.so raise_shim.c
I then execute with:
LD_PRELOAD=./raise_shim.so ruby
All of the above works well on Linux, what is the equivalent for each step to get this working on OSX? I have googled this and have not been able to get it to work with the information provided as the info for some of the steps are missing.
Thanks in advance!
Take a look at DYLD_INSERT_LIBRARIES. That's the variable you're looking for.
See also this answer.