g++比gcc对c的支持更好？？？

[cuihao]

真奇怪，我编得复杂的c程序，用gcc编译一大堆警告，g++却没事，而且貌似c99标准也支持的很好，怎么回事呀～～～

[BigSnake.NET]

贴源码。。。

[cuihao]

程序太长了，随便贴一个子函数：

代码： 全选

#include<stdio.h>
#include<math.h>
#include<string.h>

double fc(char *s,double a,double b)
{
 double rtn;

 if (strcmp(s,"abs")==0) rtn=fabs(a);
 if (strcmp(s,"ln")==0) rtn=log(a);
 if (strcmp(s,"exp")==0) rtn=exp(a);
 if (strcmp(s,"sqr")==0) rtn=a*a;
 if (strcmp(s,"sqrt")==0) rtn=sqrt(a);
 if (strcmp(s,"int")==0) rtn=trunc(a);
 if (strcmp(s,"rnd")==0) rtn=round(a);
 if (strcmp(s,"hypot")==0) rtn=hypot(a,b);

 return rtn;
}

int main(void)
{
 return 0;
}

g++编译可以，gcc出一些莫名其妙的东东：

代码： 全选

/home/cuihao/Desktop/tt.c: 在函数‘fc’中:
/home/cuihao/Desktop/tt.c:15: 警告： 隐式声明与内建函数‘trunc’不兼容
/home/cuihao/Desktop/tt.c:16: 警告： 隐式声明与内建函数‘round’不兼容
/tmp/cch40gfh.o: In function `fc':
tt.c:(.text+0x5b): undefined reference to `log'
tt.c:(.text+0x80): undefined reference to `exp'
tt.c:(.text+0xd9): undefined reference to `sqrt'
tt.c:(.text+0x104): undefined reference to `trunc'
tt.c:(.text+0x129): undefined reference to `round'
tt.c:(.text+0x155): undefined reference to `hypot'
collect2: ld 返回 1

[BigSnake.NET]

gcc a.c -std=c99 -lm

[cuihao]

喔～～～可以了～谢谢
那个-lm是什么意思

[HuntXu]

math库

[xhy]

g++只是个马甲，它用一堆参数调用了gcc

g++不是编译器，只是个外壳

[ChloeRei]

g++只是个马甲，它用一堆参数调用了gcc

g++不是编译器，只是个外壳

不是反过来么

[xhy]

g++只是个马甲，它用一堆参数调用了gcc

g++不是编译器，只是个外壳

不是反过来么

代码： 全选

man gcc

有这么一条

代码： 全选

       However, the use of gcc does not add the C++ library.  g++ is a program that calls GCC and treats .c, .h and .i files as
       C++ source files instead of C source files unless -x is used, and automatically specifies linking against the C++
       library.  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++.

[ChloeRei]

奥，原来我想错了