[英]I don't understand the behavior of fgets in this example
While I could use strings, I would like to understand why this small example I'm working on behaves in this way, and how can I fix it ? 虽然我可以使用字符串,但我想了解为什么我正在处理的这个小示例会以这种方式运行,以及如何解决?
int ReadInput() {
char buffer [5];
printf("Number: ");
fgets(buffer,5,stdin);
return atoi(buffer);
}
void RunClient() {
int number;
int i = 5;
while (i != 0) {
number = ReadInput();
printf("Number is: %d\n",number);
i--;
}
}
This should, in theory or at least in my head, let me read 5 numbers from input (albeit overwriting them). 从理论上或者至少在我的脑海中,这应该让我从输入中读取5个数字(尽管会覆盖它们)。
However this is not the case, it reads 0, no matter what. 但是事实并非如此,无论如何它都读取为0。
I understand printf puts a \\0 null terminator ... but I still think I should be able to either read the first number, not just have it by default 0. And I don't understand why the rest of the numbers are OK (not all 0). 我知道printf放置了\\ 0空终止符...但我仍然认为我应该能够读取第一个数字,而不仅仅是默认情况下为0。而且我不明白为什么其余的数字都可以(并非全为0)。
CLARIFICATION: I can only read 4/5 numbers, first is always 0. 澄清:我只能读取4/5数字,第一个始终为0。
EDIT: 编辑:
I've tested and it seems that this was causing the problem: 我已经测试过,看来这是引起问题的原因:
main.cpp main.cpp中
scanf("%s",&cmd);
if (strcmp(cmd, "client") == 0 || strcmp(cmd, "Client") == 0)
RunClient();
somehow. 不知何故。
EDIT: 编辑:
Here is the code if someone wishes to compile. 如果有人希望编译,请参见以下代码。 I still don't know how to fix 我仍然不知道如何解决
http://pastebin.com/8t8j63vj http://pastebin.com/8t8j63vj
FINAL EDIT: 最终编辑:
Could not get rid of the error. 无法摆脱错误。 Decided to simply add @ReadInput 决定只添加@ReadInput
int ReadInput(BOOL check) {
...
if (check)
printf ("Number: ");
...
@ RunClient() @ RunClient()
void RunClient() {
...
ReadInput(FALSE); // a pseudo - buffer flush. Not really but I ignore
while (...) { // line with garbage data
number = ReadInput(TRUE);
...
}
And call it a day. 并称之为一天。
fgets
reads the input as well as the newline character. fgets
读取输入以及换行符。 So when you input a number, it's like: 123\\n
. 因此,当您输入数字时,就像: 123\\n
。
atoi
doesn't report errors when the conversion fails. 转换失败时atoi
不会报告错误。
Remove the newline character from the buffer
: 从buffer
删除换行符:
buf[5];
size_t length = strlen(buffer);
buffer[length - 1]=0;
Then use strtol
to convert the string into number which provides better error detection when the conversion fails. 然后,使用strtol
将字符串转换为数字,以便在转换失败时更好地检测错误。
char * fgets ( char * str, int num, FILE * stream );
Get string from stream. 从流中获取字符串。
Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first. 从流中读取字符,并将它们作为C字符串存储到str中,直到已读取(num-1)个字符或到达换行符或到达文件末尾为止,以先发生的为准。
A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str. 换行符使fgets停止读取,但该函数将其视为有效字符并包含在复制到str的字符串中。 (This means that you carry \\n) (这意味着您携带\\ n)
A terminating null character is automatically appended after the characters copied to str. 复制到str的字符后会自动附加一个终止的空字符。 Notice that fgets is quite different from gets: not only fgets accepts a stream argument, but also allows to specify the maximum size of str and includes in the string any ending newline character. 请注意,fgets与gets有很大的不同:fgets不仅接受流参数,还允许指定str的最大大小,并在字符串中包括任何结尾的换行符。
PD: Try to have a larger buffer. PD:尝试使用更大的缓冲区。
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