Valgrind 报告 SIGSEGV 和未初始化值的使用

Question

编辑：通过初始化解决的所有 valgrind 错误 i。

我正在处理字符串；从文件中读取字符串，使用 strsep() 分隔它们，使用 atol() 将它们转换为 int。我的代码在 gcc 上编译并且运行没有错误，但是当用 valgrind 检查时我得到了标题中提到的错误。

我正在尝试使用文本文件中的 int 值填充 two-dimensional 数组 grid[20][20]。文本文件包含由空格分隔的数字行，例如 20 81 65 07 54 72 13 28 66 95 00 20 00 84 06 30 85 43 15 73\n

我的代码，（不包括所有的文件IO）如下。（请注意，我确实正确处理了文件：检查 fopen 的结果，以 fclose 结束）。

更新代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define STR_LEN     20
#define NUM_LINES   20
#define MAX_SIZE    100

int main(void){
    char input_str[MAX_SIZE];   //string to hold lines read from file
    char * str_array[STR_LEN];  //array of strings to split the lines into
    int grid[20][20];
    char * token, *str, *tofree;
    int line;
    for (line = 0; line < NUM_LINES; ++line){   //for every line in the file 
        
        if (fgets(input_str, MAX_SIZE, fp)!=NULL){  //read the file's line into input_str
            tofree = str = strdup(input_str);   //set str to copy of input_string, and tofree to point to beginning of str's memory, to free later
            
            int i = 0;
            while ((token = strsep(&str, " "))){    //split str on " ", keeping everything in between in token
                str_array[i] = token;   //add token to str_array
                ++i;
            }
            for (i = 0; i < STR_LEN; ++i){
                grid[line][i] = atol(str_array[i]); //convert strings to int and store in num_array     
                printf("grid[%d][%d]: %d\n", line, i, grid[line][i]);

            }
            free(tofree);   //free str by freeing tofree, as tofree points to str's memory
        }
    }
    printf("%d", grid[0][0]);
    return 0;
}

我用 gcc -Wall -g -c myfile.c 编译这段代码。它编译和运行都很好，没有错误。在将值传递给 grid 之后使用 printf() 检查值会显示所有正确的值。然而，代码中的最后一个 printf() 显示 grid[0][0] 包含垃圾，即使它之前是正确的。事实上，grid[0] 中的所有元素都已损坏。

运行 valgrind valgrind --leak-check=full --track-origins=yes --dsymutil=yes --show-leak-kinds=all ./productGrid.elf 给我

$ valgrind --leak-check=full --track-origins=yes --dsymutil=yes --show-leak-kinds=all ./productGrid.elf

==2252== Command: ./productGrid.elf
==2252== 
==2252== Use of uninitialised value of size 4
==2252==    at 0x106EC: main (in /home/jesse/C/Proj. Euler/productGrid.elf)
==2252==  Uninitialised value was created by a stack allocation
==2252==    at 0x10656: main (in /home/jesse/C/Proj. Euler/productGrid.elf)
==2252== 
==2252== Invalid write of size 4
==2252==    at 0x106EC: main (in /home/jesse/C/Proj. Euler/productGrid.elf)
==2252==  Address 0x7e2b6c38 is not stack'd, malloc'd or (recently) free'd
==2252== 
==2252== 
==2252== Process terminating with default action of signal 11 (SIGSEGV)
==2252==  Access not within mapped region at address 0x7E2B6C38
==2252==    at 0x106EC: main (in /home/jesse/C/Proj. Euler/productGrid.elf)
==2252==  If you believe this happened as a result of a stack
==2252==  overflow in your program's main thread (unlikely but
==2252==  possible), you can try to increase the size of the
==2252==  main thread stack using the --main-stacksize= flag.
==2252==  The main thread stack size used in this run was 8388608.
==2252== 
==2252== HEAP SUMMARY:
==2252==     in use at exit: 413 bytes in 2 blocks
==2252==   total heap usage: 3 allocs, 1 frees, 4,509 bytes allocated
==2252== 
==2252== 61 bytes in 1 blocks are still reachable in loss record 1 of 2
==2252==    at 0x483E380: malloc (vg_replace_malloc.c:299)
==2252==    by 0x48E188B: strdup (strdup.c:42)
==2252==    by 0x106C9: main (in /home/jesse/C/Proj. Euler/productGrid.elf)
==2252== 
==2252== 352 bytes in 1 blocks are still reachable in loss record 2 of 2
==2252==    at 0x483E380: malloc (vg_replace_malloc.c:299)
==2252==    by 0x48D11F3: __fopen_internal (iofopen.c:69)
==2252==    by 0x10681: main (in /home/jesse/C/Proj. Euler/productGrid.elf)
==2252== 
==2252== LEAK SUMMARY:
==2252==    definitely lost: 0 bytes in 0 blocks
==2252==    indirectly lost: 0 bytes in 0 blocks
==2252==      possibly lost: 0 bytes in 0 blocks
==2252==    still reachable: 413 bytes in 2 blocks
==2252==         suppressed: 0 bytes in 0 blocks
==2252== 
==2252== For counts of detected and suppressed errors, rerun with: -v
==2252== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 6 from 3)
Segmentation fault

对我做错了什么有什么想法吗？

Answer 1

i 在此处未初始化使用：

  str_array[i] = token; 
  ++i;

注：

如果您使用符号编译（GCC 的选项 -g），则 Valgrind 会使用对源代码行的引用来注释其日志记录。

Answer 2

我无法评论，所以我 post 一个新的答案。正如@alk 所说，i 它是未初始化的，如果您只是在定义中对其进行初始化，则 while 将不起作用。使用一个for(;;)，因为你需要赋值。

如果仍有问题，请更新您的代码。

Answer 3

你应该在开头初始化 i。

另外关于这段代码：

while ((token = strsep(&str, " "))){
    str_array[i] = token;   //add token to str_array
    ++i;
 }

for (i = 0; i < STR_LEN; ++i){
     grid[line][i] = atol(str_array[i]);
     printf("grid[%d][%d]: %d\n", line, i, grid[line][i]);
}

如果要将 i 归零，为什么要计算 i？也许你应该使用不同的计数器并循环直到这个而不是 STR_LEN.

希望对您有所帮助。

Valgrind 报告 SIGSEGV 和未初始化值的使用

Valgrind reports SIGSEGV and use of uninitialised value

c

string

valgrind

memory-leaks

更新代码