Error Correction set (continuous update)

1. Two common compression methods in Linux: (unpack: tar-zxvf + directory to be generated by package name)

Bz2 File

Time tar-jcvf j.tar.bz2 workspace/

340 m 56.8%

Real 13m20. 975 s

User 11m13. 872 s

Sys 0m5. 985 s

GZ File

Time tar-zcvf z.tar.gz workspace/

348 m 58.1%

Real 2m10. 305 S

User 0m54. 228 s

Sys 0m7. 399 s

2. when you need to add an interface or tool to a complete project, you do not have to redefine a new class. Sometimes this will become more cumbersome, you can add several functions to a defined class. This makes it clearer and more clean.

3. A dynamic link library: LDD + program name is used in the program:

        libcurl.so.4 => /usr/lib64/libcurl.so.4 (0x00007ff76c8ad000)

This is a dynamic library of curl. It supports uploading and downloading and reading webpage content. Then, when a encapsulated API is called in the program, the Protocol is not supported, that is, the HTTPS protocol, which is supported through curl-V:

curl 7.14.0 (x86_64-unknown-linux-gnu) libcurl/7.14.0 OpenSSL/1.0.1e zlib/1.2.3 libidn/1.18Protocols: ftp gopher telnet dict ldap http file https ftps Features: IDN IPv6 Largefile NTLM SSL libz 

Then the question arises. Why? Then I checked the library linked to the curl program: LDD curl:

        linux-vdso.so.1 =>  (0x00007fff7dfff000)        libcurl.so.3 => /usr/local/lib/libcurl.so.3 (0x00007f8b77c95000)        libidn.so.11 => /lib64/libidn.so.11 (0x00000036a5000000)        libssl.so.1.0.0 => /usr/local/ssl/lib/libssl.so.1.0.0 (0x00007f8b77a2b000)        libcrypto.so.1.0.0 => /usr/local/ssl/lib/libcrypto.so.1.0.0 (0x00007f8b7764f000)        libdl.so.2 => /lib64/libdl.so.2 (0x000000369b800000)        libz.so.1 => /data/mysql/lib/mysql/libz.so.1 (0x00007f8b77438000)        libc.so.6 => /lib64/libc.so.6 (0x000000369b400000)        /lib64/ld-linux-x86-64.so.2 (0x000000369b000000)        libpthread.so.0 => /lib64/libpthread.so.0 (0x000000369bc00000)        libcrypt.so.1 => /lib64/libcrypt.so.1 (0x000000369e000000)        libnsl.so.1 => /lib64/libnsl.so.1 (0x000000369f000000)        libm.so.6 => /lib64/libm.so.6 (0x000000369c000000)        libfreebl3.so => /lib64/libfreebl3.so (0x000000369dc00000)

Here we can see that the libraries used by the two programs are different, so the problem is solved.

/usr/local/lib/libcurl.so.3 

Copy

/usr/lib64/

Then Link libcurl. so.4 in the directory to libcurl. so.3 to use the correct library, and then ldconfig refreshes the cache. OK.

4. Today, I accidentally deleted a project in eclipse. I panicked and decided to go online to Baidu. I learned that the project can be recovered and my mood calmed down. The method is as follows:

In eclipse, you can restore the deleted files in the project, or restore the deleted content in a Java file like SVN.
If files in the project are deleted, follow these steps:
Right-click a project;
Select Restore from local history;
In "check files to restore from local history:", select the file to be restored.
It should be noted that there should be a cache similar to that in the eclipse recovery file. Such a cache may be limited by time and space. Therefore, if you delete too many files, it may not be restored.

I have learned some lessons over the past few days. I hope I can take a long time!

5. If a program needs to be executed in Linux Shell, when the parameter contains parentheses, such:

Cp a. Text (B). Test

An error is reported during direct use:

-Bash: syntax error near unexpected token '('

Here we need to escape the brackets in two ways:

1. Double quotation marks on both ends of the brackets:

Cp a. Test "(B)". Test

2. Add a slash to the brackets:

Cp a. Test \ (B \). Test

6. Today, the program core dump. It is found through debugging that it is a problem of negative unsigned shaping:

When defining a uint32_t type variable, pay special attention to the negative problem. When a uint32_t type variable is negative, the highest bit is changed to 1, then it will directly become the maximum, so often cause memory overflow, see: http://www.cnblogs.com/tenghoo/archive/2008/06/01/1211663.html

7. when a static map object or static vector object needs to be used in a class, that is, all class objects share one STL object or custom class object, according to the definition of C ++, static objects must be initialized outside the class implementation, but initialization of these types of objects is troublesome. Therefore, there is a solution, instead of defining a static map object in a class, the object is directly defined in the class in vitro. This not only allows the object to be used in the class, but also saves the trouble of initialization. Example:

//a.h#include <iostream>#include <map>using namespace std;class A{    public:        static A *getInstance()        {            static A a;            return &a;        }    private:        A(){}        ~A(){}            public:        void display();};

//a.cpp#include "a.h"static map<int, string>m_testMap;void A::display(){char *str[] = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};for(int i = 0; i < 7; ++i)m_testMap[i] = str[i];map<int, string>::iterator iter = m_testMap.begin();for( ; iter != m_testMap.end(); ++iter)cout << iter->second << endl;}int main(){        A::getInstance()->display();        return 0;}

Output result:

MondayTuesdayWednesdayThursdayFridaySaturdaySunday

Note: This class cannot be reentrant, that is, it is not thread-safe.