how to write a clang plugin to inject some code to the original code while compiling

问题

i got a problem about how to write a clang plugin that will change the code. i want inject some code to the program,just like this:enter code here

//the original code
//the filename is user_code.cpp
int f1(){
    return 1;
}
int f2(){
    return 2;
}
int f3(){
    return 3;
}
int main(){
   for(int i=0;i<1000;i++)f1();
   for(int i=0;i<10000;i++)f2();
   for(int i=0;i<100000;i++)f3();
   return 0;
}
//the injected code
int function_counter[3];
int f1(){
    function_counter[0]++;
    return 1;
}
int f2(){
    function_counter[1]++;
    return 2;
}
int f3(){
    function_counter[2]++;
    return 3;
}
int main(){
   for(int i=0;i<1000;i++)f1();
   for(int i=0;i<10000;i++)f2();
   for(int i=0;i<100000;i++)f3();
   return 0;
}

now, i can do this by parsing this code to an AST.and traverse it, use ReWriter class to modify the code,at last rewrite the modified code to a new file.but this is not transparent to user.i want write a clang plugin,user just input the command:

 clang -load myplugin.so -plugin myplugin user_code.cpp -o user_code.o

the code first can be injected transparently,and then compile like usualy.what can i do?any suggest?

来源：https://stackoverflow.com/questions/19346660/how-to-write-a-clang-plugin-to-inject-some-code-to-the-original-code-while-compi