Question

编辑：通过初始化i解决的所有valgrind错误。

我正在处理琴弦；从文件中读取字符串，使用strsep()进行分隔，然后使用atol()将其转换为int。我的代码在gcc上编译并运行，没有错误，但是用valgrind检查时，出现标题中提到的错误。

我正在尝试使用文本文件中的int值填充二维数组grid[20][20]。文本文件包含用空格分隔的数字行，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（不包括所有文件IO）如下。（请注意，我确实正确处理了文件：检查fopen的结果，并以fclose关闭）。

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编译此代码。它既编译又运行良好，没有错误。将值传递到printf()之后立即使用grid检查值将显示所有正确的值。但是，代码中的最后一个printf()显示grid[0][0]包含垃圾，即使以前是正确的。实际上，grid[0]中的所有元素都已损坏。

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

关于我在做什么错的任何想法吗？

Answer 1

if __name__ ==在这里未初始化使用：

注意：

如果使用符号（GCC的选项str_array[i] = token; ++i;进行编译），则Valgrind会使用对源代码行的引用来注释其日志记录。

Answer 2

我无法发表评论，所以我发布了一个新答案。正如@alk所说，i尚未初始化，如果仅在定义时对其进行初始化，则while无效。根据需要使用for(;;)。

如果仍然有问题，请更新代码。

Answer 3

您应该在开始时初始化i。

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]);
}

如果要在下面将i归零，为什么还要计算i？也许您应该使用一个不同的计数器并循环直到此而不是STR_LEN。

希望这会有所帮助。

Valgrind报告了SIGSEGV和未初始化值的使用

更新代码

3 个答案: