C中的递归不返回字符串值 [英] Recursion in C not returning string value

问题描述

我正在学习 C，为此我决定编写一个数独求解器.我无法让解决函数返回已解决的板，我认为问题出在递归函数调用上.

I am learning C and to do so I decided to write a Sudoku solver. I am having trouble getting the solve function to return a solved board and my thought is the issue is with the recursive function call.

我将棋盘作为字符串传入，找到棋盘中第一个0"的索引，并使用该索引为该位置构建一个可能值列表.然后我迭代可能性，复制原始板，并用可能性替换零，然后将新板递归地传递给求解函数.代码如下:

I pass the board in as a string, find the index of the first "0" in the board and use that index to build a list of possible values for the position. I then iterate over the possibilities, copy the original board, and replace the zero with the possibility, then pass the new board recursively to the solve function. The code is below:

char *solve(char *board)
{
    int zero = strcspn(board, "0");
    if(zero > 80) {
        return board;
    } else {
        char *possibilities = getPossibilities(zero, board);
        if(possibilities != '\0') {
            for(int i = 0; i < strlen(possibilities); i++) {
                char *new_string = malloc(strlen(board) * sizeof(char));
                memcpy(new_string, board, strlen(board));
                new_string[zero] = possibilities[i];
                return solve(new_string);
            }
        }
    }

}

理想情况下，当字符串不再有任何0"时，函数应该返回.但是我得到了一些奇怪的输出，看起来像:

Ideally, the function should return when the string no longer has any "0"'s. However I am getting some weird output that looks like:

The string is �96245781100060004504810390007950043030080000405023018010630059059070830003590007

我在看问题时遇到了麻烦.该计划的完整要点是此处.我会喜欢任何输入.提前致谢！

I having trouble eyeing the problem. The full gist of the program is here. I would love any input. Thank you in advance!

推荐答案

char *new_string = malloc(strlen(board) * sizeof(char));

需要为'\0'终止符分配，并改为

you need to allocate for the '\0' terminating character, and change it to

char *new_string = malloc(strlen(board) + 1);

并将 memcpy 更改为 strcpy

char * strcpy(new_string, board);

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