g++编译warning: deprecated conversion from string constant to ‘char*’ /tmp/ccSf0DmE.o: In function `ma

我用的ubuntu操作系统，以下是c++Primer Plus(第五版)的一段代码，结果出现了标题所示的警告，请教哪位大神帮忙解解，谢谢。

完整警告如下：

g++ strgfun.cpp -o strgfun

strgfun.cpp: In function ‘int main()’:

strgfun.cpp:6: warning: deprecated conversion from string constant to ‘char*’

/tmp/ccSf0DmE.o: In function `main':

strgfun.cpp:(.text+0x4b): undefined reference to `c_in_str(char const*, char)'

strgfun.cpp:(.text+0x5f): undefined reference to `c_in_str(char const*, char)'

collect2: ld returned 1 exit status

源码如下：

#include<iostream>

int c_in_str(const char* str, char ch);

int main(){

using namespace std;

char mmm[15] = "minimum";

char *wail = "ululate";

int ms = c_in_str(mmm, 'm');

int us = c_in_str(wail, 'u');

cout << ms << " m characters in " << mmm << endl;

cout << us << " u characters in " << wail << endl;

return 0;

}

int c_int_str(const char* str, char ch){

int count = 0;

while(*str){

if(*str == ch){

count++;

str++;

}

}

return count;

}

我尝试了把函数原型换为 int c_int_str( char* str, char ch) 和 int c_int_str( char*
const str, char ch) 仍然出现了一样的错误。