c - 更换字符串片段

Question

我正在做类似Excel的事情，我有这样的事情:

1         2           3
A1        B1          C1

其中它替换指定内容的内容，其中A1替换1的内容。B1替换2的内容...等等...

我正在使用多维数组，并且我执行如下操作:

int offset = 0, readCharCount;
    while(sscanf(matris[i][c] + offset, "%c%d%*c%n", &col, &linha, &readCharCount) == 2){
        //printf("%c, %d\n", col, linha);
        //strcpy(matris[i][c], matris[linha-1][col - 'A']);

        offset += readCharCount;
      //printf(" {%c, %d}", col, linha);
      //printf("\n");
  }

但是当我有A1+B1+C1和其他东西时，我无法替换全部内容，因为其他引用将被删除......

所以，在单元格 A1+B1+C1 处，我想将 B1 更改为指定的内容......我想要这样:

This -> A1+B1+C1

to -> 1+2+3

...

谢谢。

Answer 1

您可以重复使用此 c++ solution (通过硬编码 char* 来替换通用迭代器)。

我试了一下。但是，我想发出警告:看起来您正在尝试实现一个表达式解析器。我强烈建议你要么

• handroll(递归下降)解析器
• 使用 flex/bison(或 lex/yacc)

这样你就不会陷入在 C 语言中容易出错的文本处理的尴尬境地。

Edit: I rewrote your C program using C++; you can see it working live here.

Edit 2: Another fixup of your C program in pure C: http://ideone.com/ExnufJ updated to support iterative expansions now, too

答案只涉及纯 C 方法:

那么，让我们开始吧。我假设了一个示例“电子表格”(它可以包含数字而不是字符串):

const char* cells[][4] = {
    /* A       B           C        D                 */
    { "the"  , "lazy"    , "cow"  , "jumped"  }, /* 1 */
    { "over" , "the"     , "quick", "brown"   }, /* 2 */
    { "paper", "packages", "tied" , "up"      }, /* 3 */
    { "with" , "silver"  , "white", "winters" }, /* 4 */
    { "that" , "melt"    , "fox" ,  "springs" }, /* 5 */
};

仅使用两个助手:

const char* get_cell_value(const char* coordinate_b, const char* coordinate_e);
char* expand_cell_references(const char* f, const char* const l, char* o); /*the magic engine*/

我们可以编写以下演示程序:

int main()
{
    const char in[] = "The C2 D2 C5 D1 A2 B2 B1 dog!";

    char out[1024] = {0};
    expand_cell_references(in, in+strlen(in), out);
    puts(out); /* "The quick brown fox jumped over the lazy dog!" */

    return 0;
}

根据注释打印众所周知的测试短语。现在，get_cell_value 非常简单:

const char* get_cell_value(const char* coordinate_b, const char* coordinate_e)
{
    size_t col = 0, row = 0;
    const char* it;
    for (it=coordinate_b; it != coordinate_e; ++it)
    {
        if (*it >= 'A' && *it <= 'Z')
            col = 26*col + (*it - 'A');
        if (*it >= '0' && *it <= '9')
            row = 10*row + (*it - '0'); /* or use atoi and friends */
    }
    row--; /* 1-based row nums in Excel */

    return cells[row][col]; /* 1-based indexes in Excel */
}

并且 expand_cell_references 稍微复杂一点，是一个简单的 DFA 解析器:

char* expand_cell_references(const char* f, const char* const l, char* o)
{
    enum parser_state {
        other,
        in_coord_col,
        in_coord_row
    } state = other;

    /*temporary storage for coordinates being parsed:*/
    char accum[16] = {0};
    char* accit = accum;
    while (f!=l)
    {
        switch(state) /*dummy, the transitions flow in fallthrough order for now*/
        {
            case other:
                *(accit = accum) = 0; /*reset the accumulator*/
                while (f!=l && !(*f>='A' && *f<='Z'))
                    *o++ = *f++;
                /*fallthrough*/
            case in_coord_col:
                while (f!=l && *f>='A' && *f<='Z')
                    *accit++ = *f++;
                /*fallthrough*/
            case in_coord_row:
                {
                    const char* expanded = accum;
                    if (f!=l && *f>='0' && *f<='9')
                    {
                        while (f!=l && *f>='0' && *f<='9')
                            *accit++ = *f++;
                        expanded = get_cell_value(accum, accit);
                    }
                    else
                    {
                        *accit = 0;
                    }
                    while (*expanded)
                        *o++ = *expanded++;
                    continue; /*state = other;*/
                }
        }
    }
    return o;
}

我在那里采取了一些捷径，因为这个语法非常简单，但它应该让您正确了解从哪里开始。

See a live demo here http://ideone.com/kS7XqB so you can play with it yourself. Note that I added debugging (asserts) to the get_cell_value function so you don't accidentally reference out-of-bounds indexes.