有效的stdin阅读c编程

Question

任何人都可以帮助我优化代码读取标准输入.这就是我现在拥有的:

unsigned char *msg;
size_t msgBytes = 0;
size_t inputMsgBuffLen = 1024;
if ( (msg = (unsigned char *) malloc(sizeof(unsigned char) * inputMsgBuffLen) ) == NULL ) {
    quitErr("Couldn't allocate memmory!", EXIT_FAILURE);
}
for (int c; (c = getchar()) != EOF; msgBytes++) {
    if (msgBytes >= (inputMsgBuffLen)) {
        inputMsgBuffLen <<= 1;
        if ( ( msg = (unsigned char *)realloc(msg, sizeof(unsigned char) * inputMsgBuffLen) ) == NULL) {
            free(msg);
            quitErr("Couldn't allocate more memmory!", EXIT_FAILURE);
        }
    }
    msg[msgBytes] = (unsigned char)c;
}

Answer 1

问题:您正在阅读二进制或文本数据stdin吗？如果是文字,你为什么用unsigned char？

一些忠告:

1. 删除所有的铸件malloc和realloc; 它们不是必需的,并且使代码混乱;
2. 而不是重复调用getchar,使用fread或fgets(取决于您是否正在阅读二进制或文本);
3. 请记住,realloc可能会返回NULL,因此您希望将结果分配给临时值,否则您将丢失原始指针的跟踪并结束泄漏的内存;
4. 为每个输入块使用静态分配的缓冲区;
5. 用于sizeof对象,而不是类型; 它有点清洁,它可以保护你,以防类型发生变化(例如,T *p = malloc(sizeof *p * number_of_elements);.

假设您打算使用无符号字符的清理版本:

#define inputBufSize 1024

unsigned char *msg = NULL;
size_t msgBytes = 0;
size_t inputMsgBufSize = 0;
unsigned char inputBuffer[inputBufSize];
size_t bytesRead = 0;

while ((bytesRead = fread(
    inputBuffer,            // target buffer
    sizeof inputBuffer,     // number of bytes in buffer
    1,                      // number of buffer-sized elements to read
    stdin)) > 0)
{
  unsigned char *tmp = realloc(msg, inputMsgBufSize + bytesRead));
  if (tmp)
  {
    msg = tmp;
    memmove(&msg[inputMsgBufSize], inputBuffer, bytesRead);
    inputMsgBufSize += bytesRead;
  }
  else
  {
    printf("Ran out of memory\n");
    free(msg);
    break;
  }
}