atoi程序

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最主要的是要考虑输入条件，程序写出来了远不是面试官的目的。各种异常情况的处理、边界条件的处理，才是面试官主要考察的内容。

我所能想到的测试用例有：

1，字符串内含有非法字符，非法字符的定义为0-9，- 之外的所有字符

2，字符串表示负数

3，字符串表示的整数溢出

以下是我写的myatoi和UT

[cpp] view plaincopyprint?

#include <string.h>
int myatoi(const char* a);
void TestString(const char* str)
{
printf("%s = %d\r\n", str, myatoi(str));
}
void Test()
{
const char* test[] = {"0", "0x1","-","01", "-1","1","123","1000000000","-1000000000","100000000000","-100000000000"};
for(int i = 0; i < sizeof(test) / sizeof(const char*); i++)
{
TestString(test[i]);
}
}
int myatoi(const char* a)
{
if(a == NULL || strlen(a) == 0)
{
printf("empty string!\r\n");
return 0;
}
int t = a[0];
int i = 0;
if(t > '9' || t < '0')
{
if(t != '-')
{
printf("illegal char!\r\n");
return 0;
}
else if(strlen(a) < 2)
{
printf("illegal char!\r\n");
return 0;
}
else
{
i = 1;
}
}
for(; i < strlen(a); i++)
{
if((a[i] > '9' || a[i] < '0'))
{
printf("illegal char!\r\n");
return 0;
}
}
int sign = 1;
int pos = 0;
if(a[0] == '-')
{
sign = -1;
pos++;
}
int n = 0;
while(pos < strlen(a))
{
if(n * 10 / 10 != n)
{
printf("overflow!\r\n");
return 0;
}
n = n * 10 + (a[pos++] - '0');
}
return n * sign;
}

#include <string.h>int myatoi(const char* a);void TestString(const char* str){printf("%s = %d\r\n", str, myatoi(str));    }void Test(){const char* test[] = {"0", "0x1","-","01", "-1","1","123","1000000000","-1000000000","100000000000","-100000000000"};for(int i = 0; i < sizeof(test) / sizeof(const char*); i++){TestString(test[i]);}}int myatoi(const char* a){if(a == NULL || strlen(a) == 0){printf("empty string!\r\n");return 0;}int t = a[0];int i = 0;if(t > '9' || t < '0'){if(t != '-'){printf("illegal char!\r\n");return 0;}else if(strlen(a) < 2){printf("illegal char!\r\n");return 0;}else{i = 1;}}for(; i < strlen(a); i++){if((a[i] > '9' || a[i] < '0')){printf("illegal char!\r\n");return 0;}}int sign = 1;int pos = 0;if(a[0] == '-'){sign = -1;pos++;}int n = 0;while(pos < strlen(a)){if(n * 10 / 10 != n){printf("overflow!\r\n");return 0;}n = n * 10 + (a[pos++] - '0');}return n * sign;}

写完了以后总觉得不爽，看了看cplusplus上对atoi函数的定义，感觉这个C函数的声明本身就有问题。异常条件下返回0，这种异常处理方式很容易导致客户程序员犯下很难debug到的错误。感觉如果定义为 bool atoi(const char* a, int& i)会比较稳定。