我的公平份额malloc无效写入（以及此网站上的许多示例）但我仍然无法指出导致某些问题的原因。这里我有一个用于图形的邻接矩阵，在分配时，我从valgrind得到了无效的写入（但在整个程序中没有分段错误）。我也得到了无效的读取，但我认为这是由无效的先前写入引起的。
FYI adj_matrix是一个typedef'd结构，其顶点数为int类型，头文件中声明的实际2D数组为char **
此外，我的帖子中没有包含测试文件，它只是为结构分配空间并调用这些函数。
#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <math.h>
#include "adj_matrix.h"
void adj_matrix_init(adj_matrix *matrix, const int num_vertices) {
int i;
char* temp;
matrix->num_vertices = num_vertices;
//INVALID WRITE & READ HERE
if(!(matrix->matrix = malloc(num_vertices * sizeof(char *)))) {
fprintf(stderr, "Could not allocate space for the adjacency matrix.\n");
exit(EXIT_FAILURE);
}
// THIS ONE WORKS THOUGH
if(!(temp = calloc(num_vertices * num_vertices, sizeof(char)))) {
fprintf(stderr, "Could not allocate space for the adjacency matrix.\n");
exit(EXIT_FAILURE);
}
for(i = 0; i < num_vertices; i++) {
(matrix->matrix)[i] = temp + (i * num_vertices); // INVALID READ
}
}
void adj_matrix_destroy(adj_matrix *matrix) {
free(matrix->matrix[0]); // INVALID READ
free(matrix->matrix);
free(matrix);
}
void adj_matrix_add_edge(adj_matrix *matrix, const int from_node, const int to_node) {
matrix->matrix[from_node - 1][to_node - 1] = 1; // INVALID READ
}
void adj_matrix_remove_edge(adj_matrix *matrix, const int from_node, const int to_node) {
matrix->matrix[from_node - 1][to_node -1] = 0;
}
bool adj_matrix_check_edge(const adj_matrix *matrix, const int from_node, const int to_node) {
return (matrix->matrix[from_node - 1][to_node -1] ? true : false);
}
size_t adj_matrix_min(const size_t val1, const size_t val2) {
return (val1 <= val2) ? val1 : val2;
}
size_t adj_matrix_to_string(const adj_matrix *matrix, char *buffer, const size_t buffer_size) {
const size_t terminator = adj_matrix_min(buffer_size, (size_t)pow((matrix->num_vertices+1) + 1, 2));
int i, j, count = 0;
printf("Buffer size: %zd\nMatrix size (plus null character): %f\nMinimum: %zd\n", buffer_size, pow((matrix->num_vertices + 1), 2), terminator);
for(i = 0; i < matrix->num_vertices; i++) {
for(j = 0; j < matrix->num_vertices; j++) {
printf("TEST1: %s\n info: %d\n", buffer, matrix->matrix[i][1]); // JUST TESTING VALUES
if( (count - 1) < terminator) {
if(matrix->matrix[i][j]) {
printf("Got in with true\n");
buffer[count++] = '1';
} else {
printf("Got in with false\n");
buffer[count++] = '0';
}
buffer[count] = '\0';
}
else {
buffer[buffer_size - 1] = '\0';
return terminator;
}
printf("TEST2: %s\n", buffer);
}
if( (count - 1) < terminator ) {
buffer[count++] = '\n';
buffer[count] = '\0';
}
else {
buffer[buffer_size - 1] = '\0';
return terminator;
}
}
return terminator;
}
Valgrind的：
==5590== Memcheck, a memory error detector
==5590== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==5590== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==5590== Command: ./test-adj_matrix
==5590==
==5590== Invalid write of size 8
==5590== at 0x40080C: adj_matrix_init (adj_matrix.c:16)
==5590== by 0x400718: main (test_adjmatrix.c:12)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid read of size 8
==5590== at 0x400814: adj_matrix_init (adj_matrix.c:16)
==5590== by 0x400718: main (test_adjmatrix.c:12)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid read of size 8
==5590== at 0x4008A7: adj_matrix_init (adj_matrix.c:27)
==5590== by 0x400718: main (test_adjmatrix.c:12)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid read of size 8
==5590== at 0x400925: adj_matrix_add_edge (adj_matrix.c:39)
==5590== by 0x40072E: main (test_adjmatrix.c:14)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid read of size 8
==5590== at 0x400925: adj_matrix_add_edge (adj_matrix.c:39)
==5590== by 0x400744: main (test_adjmatrix.c:15)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid read of size 8
==5590== at 0x400925: adj_matrix_add_edge (adj_matrix.c:39)
==5590== by 0x40075A: main (test_adjmatrix.c:16)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
Buffer size: 26
Matrix size (plus null character): 25.000000
Minimum: 26
==5590== Invalid read of size 8
==5590== at 0x400A9F: adj_matrix_to_string (adj_matrix.c:62)
==5590== by 0x400772: main (test_adjmatrix.c:18)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Conditional jump or move depends on uninitialised value(s)
==5590== at 0x4E7D3B1: vfprintf (vfprintf.c:1630)
==5590== by 0x4E858D8: printf (printf.c:35)
==5590== by 0x400AD5: adj_matrix_to_string (adj_matrix.c:62)
==5590== by 0x400772: main (test_adjmatrix.c:18)
==5590== Uninitialised value was created by a heap allocation
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x4006F5: main (test_adjmatrix.c:8)
==5590==
TEST1:
info: 1
==5590== Conditional jump or move depends on uninitialised value(s)
==5590== at 0x4E7D3B1: vfprintf (vfprintf.c:1630)
==5590== by 0x4E858D8: printf (printf.c:35)
==5590== by 0x40078B: main (test_adjmatrix.c:20)
==5590== Uninitialised value was created by a heap allocation
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x4006F5: main (test_adjmatrix.c:8)
==5590==
==5590== Invalid read of size 8
==5590== at 0x400961: adj_matrix_remove_edge (adj_matrix.c:43)
==5590== by 0x4007A1: main (test_adjmatrix.c:22)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
Buffer size: 26
Matrix size (plus null character): 25.000000
Minimum: 26
==5590== Invalid read of size 8
==5590== at 0x400A9F: adj_matrix_to_string (adj_matrix.c:62)
==5590== by 0x4007B9: main (test_adjmatrix.c:24)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Conditional jump or move depends on uninitialised value(s)
==5590== at 0x4E7D3B1: vfprintf (vfprintf.c:1630)
==5590== by 0x4E858D8: printf (printf.c:35)
==5590== by 0x400AD5: adj_matrix_to_string (adj_matrix.c:62)
==5590== by 0x4007B9: main (test_adjmatrix.c:24)
==5590== Uninitialised value was created by a heap allocation
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x4006F5: main (test_adjmatrix.c:8)
==5590==
TEST1:
info: 0
==5590== Invalid read of size 8
==5590== at 0x4008E6: adj_matrix_destroy (adj_matrix.c:33)
==5590== by 0x4007C5: main (test_adjmatrix.c:26)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid read of size 8
==5590== at 0x4008F9: adj_matrix_destroy (adj_matrix.c:34)
==5590== by 0x4007C5: main (test_adjmatrix.c:26)
==5590== Address 0x51f10a8 is 0 bytes after a block of size 8 alloc'd
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400703: main (test_adjmatrix.c:10)
==5590==
==5590== Invalid free() / delete / delete[] / realloc()
==5590== at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x4007D1: main (test_adjmatrix.c:28)
==5590== Address 0x51f10a0 is 0 bytes inside a block of size 8 free'd
==5590== at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x400910: adj_matrix_destroy (adj_matrix.c:35)
==5590== by 0x4007C5: main (test_adjmatrix.c:26)
==5590==
==5590==
==5590== FILE DESCRIPTORS: 3 open at exit.
==5590== Open file descriptor 2: /dev/pts/4
==5590== <inherited from parent>
==5590==
==5590== Open file descriptor 1: /dev/pts/4
==5590== <inherited from parent>
==5590==
==5590== Open file descriptor 0: /dev/pts/4
==5590== <inherited from parent>
==5590==
==5590==
==5590== HEAP SUMMARY:
==5590== in use at exit: 26 bytes in 1 blocks
==5590== total heap usage: 4 allocs, 4 frees, 82 bytes allocated
==5590==
==5590== 26 bytes in 1 blocks are definitely lost in loss record 1 of 1
==5590== at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5590== by 0x4006F5: main (test_adjmatrix.c:8)
==5590==
==5590== LEAK SUMMARY:
==5590== definitely lost: 26 bytes in 1 blocks
==5590== indirectly lost: 0 bytes in 0 blocks
==5590== possibly lost: 0 bytes in 0 blocks
==5590== still reachable: 0 bytes in 0 blocks
==5590== suppressed: 0 bytes in 0 blocks
编辑：test_adjmatrix.c
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "adj_matrix.h"
int main() {
char* temp = malloc((5*5+1)*sizeof(char));
adj_matrix *matrix = malloc(sizeof(matrix));
adj_matrix_init(matrix, 4);
adj_matrix_add_edge(matrix, 2, 1);
adj_matrix_add_edge(matrix, 1, 2);
adj_matrix_add_edge(matrix, 3, 4);
adj_matrix_to_string(matrix, temp, (5*5+1) * sizeof(char));
printf("%s", temp);
adj_matrix_remove_edge(matrix, 1, 2);
adj_matrix_to_string(matrix, temp, (5*5+1) * sizeof(char));
adj_matrix_destroy(matrix);
free(matrix);
return 0;
}
答案 0 :(得分：7)
以下似乎不正确：
adj_matrix *matrix = malloc(sizeof(matrix));
分配4个字节（假设32位编译器）。可能应该是sizeof( adj_matrix )。