问题描述
我收到总线错误尝试读取标准输入到的char * 变量。
我只是想读的东西全过来标准输入并把它首先进入一个变量，然后继续变量工作。
I am getting "Bus Error" trying to read stdin into a char* variable.I just want to read whole stuff coming over stdin and put it first into a variable, then continue working on the variable.
我的code是如下：
char* content;
char* c;
while( scanf( "%c", c)) {
strcat( content, c);
}
fprintf( stdout, "Size: %d", strlen( content));
但不知何故，我总是得到通过调用猫的test.txt返回总线错误|的myapp ，其中的myapp 高于编译code。
But somehow I always get "Bus error" returned by calling cat test.txt | myapp, where myapp is the compiled code above.
我的问题是我如何读标准输入直到EOF到一个变量？当您在code看到的，我只是想打印输入过来标准输入的大小，在这种情况下，它应该是等于文件的大小的test.txt 。
My question is how do i read stdin until EOF into a variable? As you see in the code, I just want to print the size of input coming over stdin, in this case it should be equal to the size of the file test.txt.
我以为只是使用 scanf函数就足够了，也许缓冲方式来阅读标准输入？
I thought just using scanf would be enough, maybe buffered way to read stdin?
推荐答案
首先，你传递未初始化的指针，这意味着 scanf函数和的strcat 会写你没有自己的记忆。其次， strcat的预计两个空结尾的字符串，而C只是一个字符。这将再次导致它来阅读你没有自己的记忆。你不需要scanf的，因为你没有做任何实际的处理。最后，每次读一个字符是不必要的缓慢。这里有一个解决方案的开始，使用最后一个字符串一个可调整大小的缓冲区，并为与fgets通话的固定缓冲
First, you're passing uninitialized pointers, which means scanf and strcat will write memory you don't own. Second, strcat expects two null-terminated strings, while c is just a character. This will again cause it to read memory you don't own. You don't need scanf, because you're not doing any real processing. Finally, reading one character at a time is needlessly slow. Here's the beginning of a solution, using a resizable buffer for the final string, and a fixed buffer for the fgets call
#define BUF_SIZE 1024
char buffer[BUF_SIZE];
size_t contentSize = 1; // includes NULL
/* Preallocate space. We could just allocate one char here,
but that wouldn't be efficient. */
char *content = malloc(sizeof(char) * BUF_SIZE);
if(content == NULL)
{
perror("Failed to allocate content");
exit(1);
}
content[0] = '\0'; // make null-terminated
while(fgets(buffer, BUF_SIZE, stdin))
{
char *old = content;
contentSize += strlen(buffer);
content = realloc(content, contentSize);
if(content == NULL)
{
perror("Failed to reallocate content");
free(old);
exit(2);
}
strcat(content, buffer);
}
if(ferror(stdin))
{
free(content);
perror("Error reading from stdin.");
exit(3);
}
编辑：沃孚提到，在你输入一个NULL会导致使用与fgets时的字符串，pmaturely终止$ P $。 是一个更好的选择，如果可用，因为它处理内存的分配和做没有问题与NUL输入。
As Wolfer alluded to, a NULL in your input will cause the string to be terminated prematurely when using fgets. getline is a better choice if available, since it handles memory allocation and does not have issues with NUL input.
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