c - 如何将字符串输入到C中的数组中？

Question

我试图从用户那里获取输入(字符串)并将它们存储在一个数组中。但是在我运行这段代码后，程序立即崩溃了。

#include <stdio.h>
int main() {
    int i;
    char *word[3];
    for(i=0;i<3;i++)
    {
        printf(" Enter a word: ");
        scanf("%s", &word[i]);
    }
    printf("%s ", word[0]);
    return 0;
}

Answer 1

在这一行:

scanf("%s", &word[i]);

您需要确保 word[i]指向某处，并且有足够的空间来占据输入的字符串。自 word[i]是 char *指针，您需要在某个时候为此分配内存。否则，它只是一个不指向任何地方的悬空指针。

如果您想坚持使用 scanf() ，那么你可以预先用 malloc 分配一些空间.

malloc() allocates requested memory on the heap, then returns a void* pointer at the end.

您可以申请 malloc()在你的代码中是这样的:

size_t malloc_size = 100;

for (i = 0; i < 3; i++) {
    word[i] = malloc(malloc_size * sizeof(char)); /* allocates 100 bytes */
    printf("Enter word: ");
    scanf("%99s", word[i]); /* Use %99s to avoid overflow */
                            /* No need to include & address, since word[i] is already a char* pointer */
} 

注:必须检查 malloc() 的返回值，因为它可以返回 NULL不成功的时候。

此外，每当您使用 malloc() 分配内存时，您必须使用 free 最后释放请求的内存:

free(word[i]);
word[i] = NULL; /* safe to make sure pointer is no longer pointing anywhere */

另一种没有 scanf 的方法

更正确的读取字符串的方法应该是使用 fgets .

char *fgets(char *str, int n, FILE *stream) reads a line from an input stream, and copies the bytes over to char *str, which must be given a size of n bytes as a threshold of space it can occupy.

fgets注意事项:

附加 \n缓冲区末尾的字符。可以轻松移除。

出错时，返回 NULL .如果没有读取字符，仍然返回 NULL在末尾。

缓冲区必须静态声明为给定大小 n .

读取指定的流。来自 stdin或 FILE * .

这是一个如何使用它来读取来自 stdin 的输入行的示例。 :

char buffer[100]; /* statically declared buffer */

printf("Enter a string: ");
fgets(buffer, 100, stdin); /* read line of input into buffer. Needs error checking */

带注释的示例代码:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define NUMSTR 3
#define BUFFSIZE 100

int main(void) {
    char *words[NUMSTR];
    char buffer[BUFFSIZE];
    size_t i, count = 0, slen; /* can replace size_t with int if you prefer */

    /* loops only for three input strings */
    for (i = 0; i < NUMSTR; i++) {

        /* read input of one string, with error checking */
        printf("Enter a word: ");
        if (fgets(buffer, BUFFSIZE, stdin) == NULL) {
            fprintf(stderr, "Error reading string into buffer.\n");
            exit(EXIT_FAILURE);
        }

        /* removing newline from buffer, along with checking for overflow from buffer */
        slen = strlen(buffer);
        if (slen > 0) {
            if (buffer[slen-1] == '\n') {
                buffer[slen-1] = '\0';
            } else {
                printf("Exceeded buffer length of %d.\n", BUFFSIZE);
                exit(EXIT_FAILURE);
            }
        } 

        /* checking if nothing was entered */
        if (!*buffer) {
            printf("No string entered.\n");
            exit(EXIT_FAILURE);
        }

        /* allocate space for `words[i]` and null terminator */
        words[count] = malloc(strlen(buffer)+1);

        /* checking return of malloc, very good to do this */
        if (!words[count]) {
            printf("Cannot allocate memory for string.\n");
            exit(EXIT_FAILURE);
        }

        /* if everything is fine, copy over into your array of pointers */
        strcpy(words[count], buffer);

        /* increment count, ready for next space in array */
        count++;
    }  

    /* reading input is finished, now time to print and free the strings */
    printf("\nYour strings:\n");
    for (i = 0; i < count; i++) {
        printf("words[%zu] = %s\n", i, words[i]);
        free(words[i]);
        words[i] = NULL;
    }

    return 0;
}

示例输入:

Enter a word: Hello
Enter a word: World
Enter a word: Woohoo

输出:

Your strings:
words[0] = Hello
words[1] = World
words[2] = Woohoo