atoi不是把char*转换为int的函数吗？难道不能用吗？

Question

#include <iostream>#include <string>using namespace std ;int main ( ){string str = "123456" ;int num ;num = atoi (str.c_str( )) ;}linux下g++调试，报错：test.cpp: In function ‘int main()’:test.cpp:9: error: ‘atoi’ was not declared in this scope

Answer 1

错误的意思，你没有申明atoi这个函数。atoi的头文件是 #include <stdlib.h> 
int main（）结束要加上 return 0；

Answer 2

错误说atoi没有被声明，man atoi发现，包含atoi的头文件是stdlib.h，所以你只需要#include <stdlib.h>就可以了
[root@localhost ~]# man atoi
ATOI(3) Linux Programmer’s Manual ATOI(3)

NAME
atoi, atol, atoll, atoq - convert a string to an integer

SYNOPSIS
#include <stdlib.h>

int atoi(const char *nptr);
long atol(const char *nptr);
long long atoll(const char *nptr);
long long atoq(const char *nptr);

DESCRIPTION
The atoi() function converts the initial portion of the string pointed to by nptr to int. The behaviour is the same as.......