C : buffer and pointers

Question

我正在编写一个小程序，它必须:

1. 询问用户将输入多少个数字(动态存储在 2 个选项卡中)
2. 逐步输入数字，如果是正数，则数字进入 bufferP，如果是负数，则进入 bufferN
3. 如果缓冲区中没有更多空间，则将其大小加倍
4. 最后 printf 两个缓冲区

这是我的代码:

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

int main(){
    int length = 0;
    printf("Number of data: \n");
    scanf("%d", &length);
    int *bufferP = (int*)malloc(2*sizeof(int));
    int *bufferN = (int*)malloc(2*sizeof(int));
    int number = 0;
    for (int i = 0 ; i <= length ; i++){
        scanf("%d", &number);
        if(number < 0){
            if(*bufferN == NULL){
                printf("No more place");
                exit(0);
            }
            *bufferN= number;
            *bufferN++;
        }

        if(number >= 0){
            if(*bufferP == NULL){
                printf("No more place");

            }
            *bufferP = number;
            *bufferP++;
        }

    }

    int res =0;
    printf("tab negative : ");
    for (int i = 0; bufferN[i] != NULL; i++)
    {
        res = bufferN[i]; 
        printf("%d\n", res );
    }
    printf("tab positive : ");
    for (int i = 0; bufferP[i] != NULL; i++)
    {
        res = bufferP[i]; 
        printf("%d\n", res );
    }
}

我遇到了这些错误:

 In function ‘main’:
rev_S3_ptr.c:14:16: error: comparison between pointer and integer [-Werror]
    if(*bufferN == NULL){
                ^~
rev_S3_ptr.c:19:4: error: value computed is not used [-Werror=unused-value]
    *bufferN++;
    ^~~~~~~~~~
rev_S3_ptr.c:23:16: error: comparison between pointer and integer [-Werror]
    if(*bufferP == NULL){
                ^~
rev_S3_ptr.c:28:4: error: value computed is not used [-Werror=unused-value]
    *bufferP++;
    ^~~~~~~~~~
rev_S3_ptr.c:35:29: error: comparison between pointer and integer [-Werror]
  for (int i = 0; bufferN[i] != NULL; i++)
                             ^~
rev_S3_ptr.c:41:29: error: comparison between pointer and integer [-Werror]
  for (int i = 0; bufferP[i] != NULL; i++)

所以我的问题是:

1. 缓冲区的工作原理就像一个选项卡，对吧？那么为什么我不能直接说如果指针为空，它就已满并执行 *buffer++ ？
2. 在“没有更多的地方”，我必须将缓冲区的大小加倍，但我不知道该怎么做。

Answer 1

这个版本怎么样:

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

int main(){
    int length = 0;
    printf("Number of data: \n");
    scanf("%d", &length);
    int bufferP_size = 2, bufferP_loc = 0;
    int *bufferP = (int*)malloc(bufferP_size*sizeof(int));
    int bufferN_size = 2, bufferN_loc = 0;
    int *bufferN = (int*)malloc(bufferN_size*sizeof(int));
    int number = 0;
    for (int i = 0 ; i <= length ; i++) {
        scanf("%d", &number);
        if(number < 0) {
            if(bufferN_loc == (bufferN_size - 1)) {
                int *temp_buffer;
                printf("No more room in negative buffer, extending\n");
                bufferN_size *= 2; 
                temp_buffer = (int*)realloc(bufferN,bufferN_size*sizeof(int));
                if (temp_buffer == NULL) {
                    printf("Memory allocation failed, aborting\n");
                    free(bufferP);
                    free(bufferN);
                    exit(EXIT_FAILURE);
                }
                bufferN = temp_buffer;
            }
            bufferN[bufferN_loc++] = number;
        }

        if(number >= 0) {
            if(bufferP_loc == (bufferP_size - 1)) {
                int *temp_buffer;
                printf("No more room in positive buffer, extending\n");
                bufferP_size *= 2; 
                temp_buffer = (int*)realloc(bufferP,bufferP_size*sizeof(int));
                if (temp_buffer == NULL) {
                    printf("Memory allocation failed, aborting\n");
                    free(bufferP);
                    free(bufferN);
                    exit(EXIT_FAILURE);
                }
                bufferP = temp_buffer;
            }
            bufferP[bufferP_loc++] = number;
        }
    }

    int res =0;
    printf("tab negative : ");
    for (int i = 0; i < bufferN_loc; i++)
    {
        res = bufferN[i]; 
        printf("%d\n", res );
    }
    printf("tab positive : ");
    for (int i = 0; i < bufferP_loc; i++)
    {
        res = bufferP[i]; 
        printf("%d\n", res );
    }
    free(bufferP);
    free(bufferN);
    exit(EXIT_SUCCESS);
}

显着的变化是:

• 读入缓冲区时不要丢弃缓冲区指针的开头
• realloc 是扩展缓冲区的 friend
• 您不能使用指向缓冲区的指针来确定何时到达缓冲区的末尾，您必须自己跟踪缓冲区有多大
• 存储当前位置以及缓冲区的大小，以便您可以跟踪从何处读取和写入