link options and how g++ is invoked gcc g++

yum install gcc

yum install gcc-c++

yum reinstall gcc gcc-c++

Downloading packages:
(1/2): gcc-c++-4.8.5-28.el7_5.1.x86_64.rpm | 7.2 MB 00:00:00
(2/2): gcc-4.8.5-28.el7_5.1.x86_64.rpm | 16 MB 00:00:00
---------------------------------------------------------------------------------------------------------------------------------------------------------
Total 47 MB/s | 23 MB 00:00:00
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : gcc-4.8.5-28.el7_5.1.x86_64 1/2
Installing : gcc-c++-4.8.5-28.el7_5.1.x86_64 2/2
Verifying : gcc-4.8.5-28.el7_5.1.x86_64 1/2
Verifying : gcc-c++-4.8.5-28.el7_5.1.x86_64 2/2

Installed:
gcc.x86_64 0:4.8.5-28.el7_5.1 gcc-c++.x86_64 0:4.8.5-28.el7_5.1

Complete!
[root@txy ~]# which gcc
/usr/bin/gcc
[root@txy ~]# which g++
/usr/bin/g++

https://gcc.gnu.org/onlinedocs/gcc/Invoking-G_002b_002b.html

Next: C Dialect Options, Previous: Overall Options, Up: Invoking GCC   [Contents][Index]

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3.3 Compiling C++ Programs

C++ source files conventionally use one of the suffixes ‘.C’, ‘.cc’, ‘.cpp’, ‘.CPP’, ‘.c++’, ‘.cp’, or ‘.cxx’; C++ header files often use ‘.hh’, ‘.hpp’, ‘.H’, or (for shared template code) ‘.tcc’; and preprocessed C++ files use the suffix ‘.ii’. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).

However, the use of gcc does not add the C++ library. g++ is a program that calls GCC and automatically specifies linking against the C++ library. It treats ‘.c’, ‘.h’ and ‘.i’ files as C++ source files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a ‘.h’ extension for use in C++ compilations. On many systems, g++ is also installed with the name c++.

When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. See Options Controlling C Dialect, for explanations of options for languages related to

Using the GNU Compiler Collection (GCC): Link Options https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html

c++ - What is the difference between g++ and gcc? - Stack Overflow https://stackoverflow.com/questions/172587/what-is-the-difference-between-g-and-gcc/172592#172592

gcc and g++ are compiler-drivers of the GNU Compiler Collection (which was once upon a time just the GNU C Compiler).

Even though they automatically determine which backends (cc1 cc1plus ...) to call depending on the file-type, unless overridden with -x language, they have some differences.

The probably most important difference in their defaults is which libraries they link against automatically.

According to GCC's online documentation link options and how g++ is invoked, g++ is equivalent to gcc -xc++ -lstdc++ -shared-libgcc (the 1st is a compiler option, the 2nd two are linker options). This can be checked by running both with the -v option (it displays the backend toolchain commands being run).

gcc和g++的区别 - 苦涩的茶 - 博客园 https://www.cnblogs.com/liushui-sky/p/7729838.html

gcc和g++的区别

 

  我们在编译c/c++代码的时候，有人用gcc，有人用g++，于是各种说法都来了，譬如c代码用gcc，而c++代码用g++，或者说编译用gcc，链接用g++，一时也不知哪个说法正确，如果再遇上个extern "C"，分歧就更多了，这里我想作个了结，毕竟知识的目的是令人更清醒，而不是更糊涂。

 

误区一:gcc只能编译c代码,g++只能编译c++代码
两者都可以，但是请注意：

1.后缀为.c的，gcc把它当作是C程序，而g++当作是c++程序；后缀为.cpp的，两者都会认为是c++程序，注意，虽然c++是c的超集，但是两者对语法的要求是有区别的，例如：

#include <stdio.h>

int main(int argc, char* argv[])

{
   if(argv == 0) return;

   printString(argv);

   return;
}
int printString(char* string)

{
  sprintf(string, "This is a test.\n");
}

如果按照C的语法规则，OK，没问题，但是，一旦把后缀改为cpp，立刻报三个错：

“printString未定义”；

“cannot convert `char**' to `char*”；

”return-statement with no value“；

    这3个错分别对应前面红色标注的部分。可见C++的语法规则更加严谨一些。

 

2.编译阶段，g++会调用gcc，对于c++代码，两者是等价的，但是因为gcc命令不能自动和C＋＋程序使用的库联接，所以通常用g++来完成链接，为了统一起见，干脆编译/链接统统用g++了，这就给人一种错觉，好像cpp程序只能用g++似的。

 

误区二:gcc不会定义__cplusplus宏，而g++会
实际上，这个宏只是标志着编译器将会把代码按C还是C++语法来解释，如上所述，如果后缀为.c，并且采用gcc编译器，则该宏就是未定义的，否则，就是已定义。

 

误区三:编译只能用gcc，链接只能用g++
严格来说，这句话不算错误，但是它混淆了概念，应该这样说：编译可以用gcc/g++，而链接可以用g++或者gcc -lstdc++。因为gcc命令不能自动和C＋＋程序使用的库联接，所以通常使用g++来完成联接。但在编译阶段，g++会自动调用gcc，二者等价。

 

误区四:extern "C"与gcc/g++有关系
实际上并无关系，无论是gcc还是g++，用extern "c"时，都是以C的命名方式来为symbol命名，否则，都以c++方式命名。试验如下：
me.h：
extern "C" void CppPrintf(void);

 

me.cpp:
#include <iostream>
#include "me.h"
using namespace std;
void CppPrintf(void)
{
     cout << "Hello\n";
}

 

test.cpp:
#include <stdlib.h>
#include <stdio.h>
#include "me.h"        
int main(void)
{
    CppPrintf();
    return 0;
}

 

1. 先给me.h加上extern "C"，看用gcc和g++命名有什么不同
[root@root G++]# g++ -S me.cpp     //g++的参数-S： 是指把文件编译成为汇编代码
[root@root G++]# less me.s
.globl _Z9CppPrintfv        //注意此函数的命名
        .type   CppPrintf, @function

[root@root GCC]# gcc -S me.cpp
[root@root GCC]# less me.s
.globl _Z9CppPrintfv        //注意此函数的命名
        .type   CppPrintf, @function
完全相同！
               
2. 去掉me.h中extern "C"，看用gcc和g++命名有什么不同
[root@root GCC]# gcc -S me.cpp
[root@root GCC]# less me.s
.globl _Z9CppPrintfv        //注意此函数的命名
        .type   _Z9CppPrintfv, @function

[root@root G++]# g++ -S me.cpp
[root@root G++]# less me.s
.globl _Z9CppPrintfv        //注意此函数的命名
        .type   _Z9CppPrintfv, @function
完全相同！

【结论】完全相同，可见extern "C"与采用gcc/g++并无关系，以上的试验还间接的印证了前面的说法：在编译阶段，g++是调用gcc的。

转自：http://lpy999.blog.163.com/blog/static/117372061201182042232511/