c - 如何在 C 中为字符串数组分配内存 - malloc 错误

Question

问题: 我想为固定大小的字符串数组的元素分配内存，但是，我有 75% 的时间遇到​​崩溃。

那是我的程序运行完美的 25%，但错误是我以前没有遇到过的

#define PACKAGE_COUNT 60
#define MAX_COUNT     5

const char *colors[] = { "blue", "red", "yellow", "purple", "orange" };

char **generatePackage() {


  char **generatedPackage = malloc(PACKAGE_COUNT);
  int randomIndex         = 0;

  for (int i = 0; i <= PACKAGE_COUNT; ++i) {

    randomIndex         = rand() / (RAND_MAX / MAX_COUNT + 1);
    generatedPackage[i] = malloc(sizeof(char) * sizeof(colors[randomIndex])); 
    // ERROR

    strcpy((generatedPackage[i]), colors[randomIndex]);

    // printf("generatePackage - %d: %s \n", i + 1, generatedPackage[i]);
  }

  return generatedPackage;
}

Answer 1

您没有考虑到指针的大小不是一个这一事实。因此，只分配了一小部分大小。因此，一些指针没有足够的内存分配，导致程序仅在访问其中一个时崩溃。

#define PACKAGE_COUNT 60
#define MAX_COUNT     5

const char *colors[] = { "blue", "red", "yellow", "purple", "orange" };

char **generatePackage() {
  char **generatedPackage = malloc(PACKAGE_COUNT * sizeof(char*)); // The size of a pointer is not one, so this a multiplicative factor must be applied
  int randomIndex         = 0;

  for (int i = 0; i < PACKAGE_COUNT; ++i) { // the upper bound is i < PACKAGE_COUNT, not i <= PACKAGE_COUNT

    randomIndex         = rand() / (RAND_MAX / MAX_COUNT + 1);
    generatedPackage[i] = malloc(sizeof(char) * (strlen(colors[randomIndex]) + 1)); // You probably want to allocate enough space for the string, rather than enough space for the pointer, so you must use strlen

    strcpy((generatedPackage[i]), colors[randomIndex]);

    // printf("generatePackage - %d: %s \n", i + 1, generatedPackage[i]);
  }

  return generatedPackage;
}