C++实现词法分析器
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#include
#include
using namespace std;
char inchar[80], token[8];
char character;
int zbbm, p, m = 0, n, row, sum = 0;
char *blz[6] = { "while", "if", "else", "switch", "case" };
void input()
{
for (n = 0; n<8; n++) token[n] = NULL;
character = inchar[p++];
while (character == ' ')
{
character = inchar[p];
p++;
}
if ((character >= 'a'&&character <= 'z') || (character >= 'A'&&character <= 'Z'))
{
m = 0;
while ((character >= '0'&&character <= '9') || (character >= 'a'&&character <= 'z') || (character >= 'A'&&character <= 'Z'))
{
token[m++] = character;
character = inchar[p++];
}
token[m++] = '\0';
p--;
zbbm = 6;
for (n = 0; n<5; n++)
if (strcmp(token, blz[n]) == 0)
{
zbbm = n + 1;
break;
}
}
else if ((character >= '0'&&character <= '9'))
{
{
sum = 0;
while ((character >= '0'&&character <= '9'))
{
sum = sum * 10 + character - '0';
character = inchar[p++];
}
}
p--;
zbbm = 7;
if (sum>32767)
zbbm = -1;
}
else switch (character)
{
case'<':m = 0; token[m++] = character;
character = inchar[p++];
if (character == '=')
{
zbbm = 11;
token[m++] = character;
}
else
{
zbbm = 11;
p--;
}
break;
case'=':m = 0; token[m++] = character;
character = inchar[p++];
if (character == '=')
{
zbbm = 11;
token[m++] = character;
}
else
{
zbbm = 12;
p--;
}
break;
case'+':zbbm = 8; token[0] = character; break;
case'-':zbbm = 9; token[0] = character; break;
case'*':zbbm = 10; token[0] = character; break;
case';':zbbm = 13; token[0] = character; break;
case'#':zbbm = 0; token[0] = character; break;
default: zbbm = -1; break;
}
}
int main()
{
p = 0;
row = 1;
cout << "请输入字符串:" << endl;
do
{
cin.get(character);
inchar[p++] = character;
} while (character != '#');
p = 0;
do
{
input();
switch (zbbm)
{
case 7: cout << "(" << zbbm << "," << sum << ")" << endl; break;
case -1: cout << "Error in row " << row << "!" << endl; break;
case -2: row = row++; break;
default: cout << "(" << zbbm << "," << token << ")" << endl; break;
}
} while (zbbm != 0);
system("pause");
}