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Combine two or more columns in a dataframe into a new column with a new name
...f$s)
df
# n s b x
# 1 2 aa TRUE 2 aa
# 2 3 bb FALSE 3 bb
# 3 5 cc TRUE 5 cc
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Linux反编译全攻略 - 操作系统(内核) - 清泛网 - 专注C/C++及内核技术
...在目录。运行“ objdump -x cm2 ”，显示如下：
代码:
[ncc2008@localhost]$ objdump -x cm2
cm2: file format elf32-i386
cm2
architecture: i386, flags 0x00000102:
EXEC_P, D_PAGED
start address 0x08048080
程序头：
LOAD off 0x00000000 vaddr 0x08048000 paddr 0x...
Resolve build errors due to circular dependency amongst classes
... A.h
class A {
B _b;
};
// file: B.h
class B {
A _a;
};
// file main.cc
#include "A.h"
#include "B.h"
int main(...) {
A a;
}
When you are compiling the .cc file (remember that the .cc and not the .h is the unit of compilation), you need to allocate space for object A. So, well, how much sp...
What's the difference between := and = in Makefile?
...
A simple assignment expression is evaluated only once, at the very first occurrence.
For example, if CC :=${GCC} ${FLAGS} during the first encounter is evaluated to gcc -W then
each time ${CC} occurs it will be replaced with gcc -W.
Recursive assignment =
A Recursive assignment expression is ev...
How to open, read, and write from serial port in C?
... tty.c_oflag = 0; // no remapping, no delays
tty.c_cc[VMIN] = 0; // read doesn't block
tty.c_cc[VTIME] = 5; // 0.5 seconds read timeout
tty.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl
tty.c_cflag |= (CLOCA...
google mock分享（全网最全最好的gmock文档，没有之一） - C/C++ - 清泛网 ...
...果是一个形参，就是MOCK_METHOD1了，以此往下。
FooMain.cc
#include <cstdlib>
#include <gmock/gmock.h>
#include <gtest/gtest.h>
#include <iostream>
#include <string>
#include "MockFoo.h"
using namespace seamless;
using namespace std;
using ::testing::Return;...
Single quotes vs. double quotes in C or C++
...instance:
const uint32_t png_ihdr = 'IHDR';
The resulting constant (in GCC, which implements this) has the value you get by taking each character and shifting it up, so that 'I' ends up in the most significant bits of the 32-bit value. Obviously, you shouldn't rely on this if you are writing plat...
What techniques can be used to speed up C++ compilation times?
...ry. This is a good place for STL headers and other library include files.
ccache is another utility that takes advantage of caching techniques to speed things up.
Use Parallelism
Many compilers / IDEs support using multiple cores/CPUs to do compilation simultaneously. In GNU Make (usually used wi...
When to use dynamic vs. static libraries
...o2();
}
$$:~/static [37]> cat makefile
hello: hello.o libtest.a
cc -o hello hello.o -L. -ltest
hello.o: hello.c
cc -c hello.c -I`pwd`
libtest.a:foo.o foo2.o
ar cr libtest.a foo.o foo2.o
foo.o:foo.c
cc -c foo.c
foo2.o:foo.c
cc -c foo2.c
clean:
rm -f ...
How to change the default GCC compiler in Ubuntu?
I have installed gcc-3.3/g++-3.3 on ubuntu 11.04 which already has gcc/g++-4.4. So in my system both gcc-3.3 and 4.4 are available. I am able to call both compilers as I want. If I just call the command gcc then gcc-4.4 will get called. To call gcc-3.3, I have to use the command gcc-3.3 .
...