#include <stdio.h>

int main()
{
    char str1[300] = {0};
    char str2[300] = {0};
    char out[300] = {0};
    gets(str1);
    gets(str2);
    /* 固定str1为最短的字符串 */
    if(strlen(str1) > strlen(str2))
    {
        char temp[300] = {0};
        strcpy(temp, str1);
        strcpy(str1, str2);
        strcpy(str2, temp);
    }
    int len1 = strlen(str1);
    int len2 = strlen(str2);
    int max = 0;
    int count = 0;
    for(int i = 0; i < len1; i++)    //输出开头
    {
        for(int j = 0;j < len2; j++)
        {
            count = 0;
            while(str1[i+count] == str2[j+count] && str1[i+count] != '\0')
            {
                count++;
            }
            if(max < count)
            {
                max = count;    //输出结尾
                //printf("i:[%d], max:[%d], str1:[%s]\n", i, max, str1+i);
                strcpy(out, str1+i);
                out[max] = '\0';
            }
        }
    }
    printf("%s\n", out);
    return 0;
}
示例:
str1 = abcdefghijklmnop
str2 = abcsafjklmnopqrstuvw
/*
i 表示从哪个位置开始
max 表示有几个字符符合要求
*/
i:[0], max:[3], str1:[abcdefghijklmnop]
i:[9], max:[7], str1:[jklmnop]
jklmnop