c - 使用通配符 (*) 作为第一个输入时，程序出现段错误

Question

/*Input string argument can be up to 3 integer numbers, 
  separated by spaces.  A wild card value, represented by a * 
  character can replace any one of the integer numbers.*/

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>

void parse(char *data);

int program = 0, version = 0, process = 0;

unsigned char flags = 0;

#define GOT_PROG 0x01

#define GOT_VERS 0x02

#define GOT_PROC 0x04


int main()

{
    char data[] = " * 10 7 ";
    parse(data);
    system("PAUSE");
    return 0;
}


void parse(char *data)
{

    char *tmp = NULL;
    /* advance past whitespace */
    while(isspace((int)*data)) data++;
    if(*data != '*')
    {
        program = strtoul(data,&tmp,0);
        flags|=GOT_PROG;
        printf("%d 11\n",program );
    }

    if(*tmp == '\0') return;
    data=++tmp;

    if(*data != '*')
    {
        version = strtoul(data,&tmp,0);
        flags|=GOT_VERS;
        printf("%d  22\n",version);
    }
    else
    {
        tmp++;
    }

    if(*tmp == '\0') return;
    data=++tmp;

    if(*data != '*')
    {
        process = strtoul(data,&tmp,0);
        flags|=GOT_PROC;
        printf("%d  33\n",process);
    }
}

当我的输入是 3 个整数时，它运行良好。当我的输入是两个整数和一个 * 时，它运行正常，除非我用 * 替换第一个整数，不知道我哪里出错了!有什么建议吗？

Answer 1

此 block 中的逻辑错误:

char *tmp = NULL;
/* advance past whitespace */
while(isspace((int)*data)) data++;

// If *data == '*', you are skipping the code inside the if block.
// tmp continues to be NULL.
if(*data != '*')
{
    program = strtoul(data,&tmp,0);
    flags|=GOT_PROG;
    printf("%d 11\n",program );
}

// Now you are dereferencing a NULL pointer
// and then setting the value of data to 'NULL + 1'.

if(*tmp == '\0') return;
data=++tmp;

我没有遵循您函数的整个逻辑，但您必须添加处理 *data == '*' 情况的代码。