[英]fscanf not reading strings into array
Why doesn't this main print anything? 为什么这个主要印刷品什么都没有? It should print the first word in the file. 它应该打印文件中的第一个单词。
int main(int argc, char *argv[])
{
FILE *file = fopen(argv[1], "r");
int n = atoi(argv[2]);
char **words = new char*[n];
for(int i = 0; i < n; i++)
{
fscanf(file, "%s ", words[i]);
}
cout << words[0] << endl;
}
words[i]
is a pointer that points to a random memory location. words[i]
是指向随机存储器位置的指针。 Make sure to make it point to allocated memory. 确保使其指向分配的内存。
//Now words[i] points to the 1000 bytes allocated with the new keyword
words[i] = new char[1000];
//fscan will write the input to those bytes
fscanf(file, "%s ", words[i]);
char **words = new char*[n];
will allocate a buffer to hold n pointers to char, words
is just a pointer to an array of pointers. 将分配一个缓冲区来保存n个指向char的指针, words
只是指向指针数组的指针。 You need allocate enough memory for words[i]
(the pointer to ) to hold the string: 您需要为words[i]
(指向的指针)分配足够的内存以容纳字符串:
for (i=0; i < n; ++i ) {
words[i] = new char[your_max_string_len];
}
Optionally you can use getline
extension of GNU (if you use gcc) to do what you want: (可选)您可以使用GNU的 getline
扩展 (如果使用gcc)来执行所需的操作:
size_t len = 0;
ssize_t read;
read = getline(&words[i], &len, stdin);
...
free(words[i]);
Actually, there is no magic in this function, it just does the memory allocation under the hood to save yours, and it's your responsibility to free it. 实际上,此功能没有魔术,它只是在后台进行内存分配以保存您的内存,而您有责任释放它。
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