c - Valgrind:未初始化的值

Question

下面的代码是一个迷宫问题程序。我可以成功地获取路径的方向。但是，当我使用 valgrind 检查我的代码时，出现了一些问题。

代码:

001: #include <stdio.h>
002: #include <stdlib.h>
003: #include <string.h>
004: 
005: struct each_path {
006:     int step_nums, coin_nums;
007:     int step_assume_num;
008:     // char **step_dir;
009:     char step_dir[100][100];
010: };
011: 
012: void initialized_params();
013: void *readFile(char *fileName);
014: void maze_1Dto2D(char *array);
015: void visit(int, int);
016: void display_direction();
017: struct each_path epath[100];
018: int path_assume_num;
019: char maze1D[5000], maze2D[1000][1000], maze2D_tmp[1000][1000];
020: int maze_height, maze_width;
021: int startI = 1, startJ = 1, endI, endJ;  // entrance & exit
022: int path_nums, coin_nums, min_step_num, min_path_num;
023: 
024: int main(void) {
025:     int i;
026: 
027:     initialized_params();
028:     // read map
029:     readFile("maze1.txt");
030:     for ( i = 0; i < maze_height; ++i ) {
031:         memcpy(maze2D_tmp[i], maze2D[i], maze_width + 1);
032:     }
033: 
034:     endI = maze_height - 2;
035:     endJ = maze_width - 2;
036:     visit(startI, startJ);
037: 
038:     exit(0);
039: }

078: void maze_1Dto2D(char *array) {
079:     size_t i = 0, j = 0, num = 0;
080: 
081:     for ( i = 0; i < maze_height ; ++i)
082:     {
083:         for ( j = 0; j < maze_width + 1; ++j, ++num)
084:         {
085:             maze2D[i][j] = array[num];
086: 
087:             if (array[num] == '\r')
088:                 --j;
089:             else if (array[num] == '\n')
090:                 maze2D[i][j] = '\0';
091:             else
092:                 maze2D[i][j] = array[num];
093:         }
094:     }
095: }
096: 
097: void visit(int i, int j) {
098:     int preI, preJ, curI = 1, curJ = 1;
099:     int step_nums = 0, step_assume_num = 10; // entrance is not included
100:     char dir[6];
101:     int m, n;
102: 
103:     if (maze2D_tmp[i][j] == '2')
104:         coin_nums++;
105:     maze2D_tmp[i][j] = '3';
106: 
107:     if (i == endI && j == endJ) {
108:         if (path_nums >= path_assume_num) {
109:             path_assume_num *= 2;
110: 
111:             epath[path_nums].step_assume_num = step_assume_num;
112:         }
113:         while (curI != endI || curJ != endJ)
114:         {
115: 
116:             if ( maze2D_tmp[curI][curJ + 1] == '3' && preJ != (curJ + 1) ) {
117:                 preI = curI;
118:                 preJ = curJ;
119:                 curJ++;
120:                 strcpy(dir, "right");
121: 
122:             }
123:             else if ( maze2D_tmp[curI + 1][curJ] == '3' && preI != (curI + 1) ) {
124:                 preI = curI;
125:                 preJ = curJ;
126:                 curI++;
127:                 strcpy(dir, "down");
128:             }
129:             else if ( maze2D_tmp[curI - 1][curJ] == '3' && preI != (curI - 1) ) {
130:                 preI = curI;
131:                 preJ = curJ;
132:                 curI--;
133:                 strcpy(dir, "up");
134:             }
135:             else if ( maze2D_tmp[curI][curJ - 1] == '3' && preJ != (curJ - 1)) {
136:                 preI = curI;
137:                 preJ = curJ;
138:                 curJ--;
139:                 strcpy(dir, "left");
140:             }
141:             strcpy(epath[path_nums].step_dir[step_nums], dir);
142:             step_nums++;
143:         }
144:         epath[path_nums].step_nums = step_nums;
145:         epath[path_nums].coin_nums = coin_nums;
146:         path_nums++;
147:         if (step_nums < min_step_num)
148:         {
149:             min_step_num = step_nums;
150:             min_path_num = path_nums;
151:         }
152:     }
153: 
154:     if (maze2D_tmp[i][j + 1] == '1' || maze2D_tmp[i][j + 1] == '2') visit(i, j + 1);
155:     if (maze2D_tmp[i + 1][j] == '1' || maze2D_tmp[i + 1][j] == '2') visit(i + 1, j);
156:     if (maze2D_tmp[i][j - 1] == '1' || maze2D_tmp[i][j - 1] == '2') visit(i, j - 1);
157:     if (maze2D_tmp[i - 1][j] == '1' || maze2D_tmp[i - 1][j] == '2') visit(i - 1, j);
158: 
159:     if (maze2D[i][j] == '2')
160:     {
161:         maze2D_tmp[i][j] = '2';
162:         coin_nums--;
163:     }
164:     else
165:         maze2D_tmp[i][j] = '1';
166: }

我想问一下为什么我从 Valgrind 得到下面两句话! “条件跳转或移动取决于未初始化的值” “未初始化的值是由堆栈分配创建的”

Valgrind 报告

==25816== Conditional jump or move depends on uninitialised value(s)
==25816==    at 0x400B4B: visit (mazeproblemA.c:123)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D9A: visit (mazeproblemA.c:155)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D3E: visit (mazeproblemA.c:154)
==25816==    by 0x400D9A: visit (mazeproblemA.c:155)
==25816==    by 0x400D9A: visit (mazeproblemA.c:155)
==25816==    by 0x400DF6: visit (mazeproblemA.c:156)
==25816==  Uninitialised value was created by a stack allocation
==25816==    at 0x4009E3: visit (mazeproblemA.c:97)

Answer 1

当您第一次在 visit 函数中进入 while 循环时，变量 preI 和 preJ 还没有尚未初始化。然后，while 内的 if 语句读取那些未初始化的值。这就是 valgrind 所提示的。

您需要为这些变量赋予有意义的初始值，也许是 0。