volatile
不用 cpu register ，每次从内存读， needed for memory-mapped I/O
ccls/clangd
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| cmake -H. -BDebug -DCMAKE_BUILD_TYPE=Debug -DCMAKE_EXPORT_COMPILE_COMMANDS=YES -DCONAN_DISABLE_CHECK_COMPILER=YES
ln -s Debug/compile_commands.json
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type convert
C++
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| using namespace std;
int z = 13;
string s = to_string(z);
int m = stoi(s);
cout << s << endl;
cout << m << endl;
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C
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| char* x = "1234567890";
long y = atol(x);
char* z = "1.234567890";
double u = strtod(z, NULL);
printf("%d\n",y);
printf("%g",z);
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product type
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| using namespace std;
auto n = std::make_tuple(1, 'c', "fsadf");
auto ll = get<2>(n);
cout << get<0>(n);
cout << get<1>(n);
cout << get<2>(n) << endl;
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C++ type size
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| using namespace std;
auto num_bytes_signed = sizeof(signed int);
auto min_signed = std::numeric_limits<signed int>().min();
auto max_signed = std::numeric_limits<signed int>().max();
auto num_bytes_unsigned = sizeof(unsigned int);
auto min_unsigned = std::numeric_limits<unsigned int>().min();
auto max_unsigned = std::numeric_limits<unsigned int>().max();
std::cout << "int bytes (signed): " << num_bytes_signed << '\n';
std::cout << "min value (signed): " << min_signed << '\n';
std::cout << "max value (signed): " << max_signed << '\n';
std::cout << '\n';
std::cout << "int bytes (unsigned): " << num_bytes_unsigned << '\n';
std::cout << "min value (unsigned): " << min_unsigned << '\n';
std::cout << "max value (unsigned): " << max_unsigned << '\n';
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%x 即按十六进制输出，英文字母小写，右对齐。
%02X 有以下变化：英文字母变大写，如果输出字符不足两位的，输出两位宽度，右对齐，空的一位补 0。超过两位的，全部输出。
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| unsigned int x = {0x7f, 0xAB0, 0xA0A0, 0xFAFA, 0x100};
x = ~ x;
int arr[4]={1,2,3,4};
int *ptr1=(int *)(&arr+1);
int *ptr2=(int *)((int)arr+1);
int (*arrp)[4]= 0x64;
int *parr[5]={0x64, 0xAB0, 0xA0A0, 0xFAFA, 0x100};
int i;
printf("hello world ddd %x\n", x);
printf("Array elements are\n");
for(i=0;i<5;i++)
printf("Arrp Decimal: %d, Hex: %X\n", arrp , arrp + i);
for(i=0;i<5;i++)
printf("Parrallel Decimal: %d, Hex: %X\n",parr[i],parr[i]);
printf("%x %x %x\n",&arr,ptr1,ptr2);
printf("%016x",ptr1);
return 0;
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C str
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| using namespace std;
const char* eee = "fsdaf";
cerr << eee << endl;
while (*eee != '\0') {
cout << *eee << endl;
++eee;
}
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Multi-thread
2 thread add to one number alternatively
atomic
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| using namespace std;
atomic_int e = 0;
auto ff = [&e](string x, int i) {
while (e < 20) {
if (e % 2 == i) {
cout << x << " : " << e << endl;
e.fetch_add(1);
}
}
};
thread dd(ff, "d", 0);
thread ee(ff, "e", 1);
dd.join();
ee.join();
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conditional variable
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| using namespace std;
std::mutex mu;
std::condition_variable cv;
vector<int> myvector{5, 4, 6, 7, 9, 3, 10, 9, 5, 6};// myvector: 99 99 99 99
auto f = [&](string x) {
while (1) {
unique_lock<mutex> um(mu);
if (myvector.size() != 0) {
cout << x << " : " << myvector.front() << endl;
myvector.erase(myvector.begin());
cv.notify_one();
cv.wait(um);
} else {
// close other thread
cv.notify_one();
break;
}
}
};
thread a(f, "a");
thread b(f, "b");
cv.notify_one();
a.join();
b.join();
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future
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| cout << "main thread id is :" << this_thread::get_id() << endl;
vector<future<void> > futures;
for (int i = 0; i < 10; ++i) {
futures.emplace_back(async([]() {
this_thread::sleep_for(chrono::seconds(2));
cout << this_thread::get_id() << endl;
}));
}
for_each(futures.begin(), futures.end(),
[=](future<void> &fut) { fut.wait(); });
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Left and righ value
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| std::string s1 = "Test";
std::string& r1 = s1;// 错误：不能绑定到左值
const std::string& r2 = s1;// 可行：到常值的左值引用延长生存期
// r2 += "Test"; // 错误：不能通过到常值的引用修改
std::string&& r3 = s1 + s1;// 可行：右值引用延长生存期
r3 += "Test";// 可行：能通过到非常值的右值引用修改
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| vector<int> myints{10, 20, 50, 30, 40};
auto myints_it = myints.begin();
vector<int> myvector{5, 4, 6, 7, 9,
3, 10, 9, 5, 6};
iter_swap(myints_it + 3, myvector.begin() + 2);
partial_sort(myints_it, myints_it + 3, myints_it + 4, less<int>());
for (auto x : myints) {
cout << x << endl;
}
cout << "\n";
for (auto x : myvector) {
cout << x << endl;
}
int sum = std::accumulate(myints.begin(), myints.end(), (int)0);
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C Duff’s device
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| #define crBegin static int state=0; switch(state) { case 0:
#define crReturn(i,x) do { state=i; return x; case i:; } while (0)
#define crFinish }
int function(void) {
static int i;
crBegin;
for (i = 0; i < 10; i++)
crReturn(1, i);
crFinish;
}
int main() {
printf("start %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("run %d \n", function());
printf("finished %d \n", function());
//printf(function());
return 0;
}
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C set jump/long jump
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| static jmp_buf buf;
static jmp_buf buf2;
void second(void) {
int stack_variable = 200;
printf("second\n"); // 打印
setjmp(buf2);
printf("stack_variable after long jump down is %d, ", stack_variable);
longjmp(buf,1); // 跳回setjmp的调用处 - 使得setjmp返回值为1
}
void first(void) {
second();
printf("first\n"); // 不可能执行到此行
}
int main() {
static int loop_times = 5;
int stack_variable = 100;
if ( ! setjmp(buf) ) {
first(); // 进入此行前，setjmp返回0
} else { // 当longjmp跳转回，setjmp返回1，因此进入此行
printf(" main\n"); // 打印
}
printf("stack_variable after long jump up is %d ,", stack_variable);
while(1) {
--loop_times;
if(loop_times <0) break;
longjmp(buf2,1);
}
return 0;
}
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