是GETC（）定义它返回EOF之后？ [英] Is getc() defined after it has returned EOF?
问题描述
我用 GETC（）; 在C锻炼; Tibial，并回头看我发现了一些奇怪的程序后。我以为，在命令行参数给出的文件包含至少一个字节。 （它调用 GETC（）; 连续两次不检查 EOF 尝试它在一个空文件，它之后。仍然工作顺利我的问题是：是 GETC（）的行为; 文件指针一个已经耗尽（EOF已经达到，而不是复卷）未定义或将它总是不断地返回EOF？
我想我可能会扩大这个问题在C STL所有的I / O功能，请在你的答案也澄清这一点。
下面是code的程序。该计划应该剥去所有评论的C / C ++源文件（和它的作品完美）。
的#include＆LT;＆stdio.h中GT;INT主（INT ARGC，CHAR *的argv []）{
INT状态= 0; //状态：0 =正常，1 =字符串2 =在评论中块注释3 =
INT ignchar = 0; //字符数忽视
INT CUR，接下来的; //当前字符与下一个
FILE * FP; //输入文件 如果（的argc == 1）{
fprintf中（标准错误，用法：％s的file.c中\\ n，argv的[0]）;
返回1;
} 如果（（FP = FOPEN（的argv [1]，R））== NULL）{
fprintf中（标准错误，打开文件时出错\\ n）;
返回2;
} CUR = GETC（FP）; //初始化CUR，假定该文件包含至少一个字节
而（（NEXT = GETC（FP））！= EOF）{
开关（下）{
案件 '/'：
如果（国家＆安培;！＆安培; CUR =='/'）{
状态= 2; //启动评论
ignchar = 2; //不打印此也不下一个字符（//）
}否则如果（状态== 3安培;＆安培; CUR =='*'）{
状态= 0; //块注释结束
ignchar = 2; //不打印此也不下一个字符（* /）
}
打破;
案件 '*'：
如果（国家＆安培;！＆安培; CUR =='/'）{
状态= 3; //块注释开始
ignchar = 2; //不打印此也不下一个字符（/ *）
}
打破;
情况下的'\\ n'：
如果（状态== 2）{
状态= 0;
ignchar = 1; //不打印当前的字符（现仍然在评论）
}
打破;
案件 ''：
如果（状态== 0）{
状态= 1;
}否则如果（状态== 1）{
状态= 0;
}
} 如果（国家＆LT; = 1＆安培;＆安培;！ignchar）的putchar（现）;
如果（ignchar）ignchar--;
CUR =下一个;
} 返回0;
}
标准输入输出文件保持这种被设置在第一时间结束文件达到，只能通过调用重置EOF标志的clearerr 或执行一个成功的 fseek的或退。因此，一旦 GETC 收益 EOF 一次，它会回头率 EOF ，即使新的数据可用，除非您使用上述方法之一清除EOF标志。
一些不符合标准的实现可以立即做出新的可用数据。此行为是有害的，可以打破一致性的应用程序。
I use getc(); in a C excercise, and after looking back on the program I noticed something weird. I assumed that the file given on the command line arguments contains at least one byte. (It calls getc(); twice in a row without checking for EOF. After trying it on an empty file it still worked smoothly. My question is: is the behaviour of getc(); on a file pointer that's been exhausted (EOF has been reached and not rewinded) undefined or will it always continue to return EOF?
I think I could expand this question to all the I/O functions in the C STL, please clarify this in your answer too.
Here is the code for the program. The program is supposed to strip a C/C++ source file from all comments (and it works perfectly).
#include <stdio.h>
int main(int argc, char *argv[]) {
int state = 0; // state: 0 = normal, 1 = in string, 2 = in comment, 3 = in block comment
int ignchar = 0; // number of characters to ignore
int cur, next; // current character and next one
FILE *fp; // input file
if (argc == 1) {
fprintf(stderr, "Usage: %s file.c\n", argv[0]);
return 1;
}
if ((fp = fopen(argv[1], "r")) == NULL) {
fprintf(stderr, "Error opening file.\n");
return 2;
}
cur = getc(fp); // initialise cur, assumes that the file contains at least one byte
while ((next = getc(fp)) != EOF) {
switch (next) {
case '/':
if (!state && cur == '/') {
state = 2; // start of comment
ignchar = 2; // don't print this nor next char (//)
} else if (state == 3 && cur == '*') {
state = 0; // end of block comment
ignchar = 2; // don't print this nor next char (*/)
}
break;
case '*':
if (!state && cur == '/') {
state = 3; // start of block comment
ignchar = 2; // don't print this nor next char (/*)
}
break;
case '\n':
if (state == 2) {
state = 0;
ignchar = 1; // don't print the current char (cur is still in comment)
}
break;
case '"':
if (state == 0) {
state = 1;
} else if (state == 1) {
state = 0;
}
}
if (state <= 1 && !ignchar) putchar(cur);
if (ignchar) ignchar--;
cur = next;
}
return 0;
}
Stdio files keep an "eof" flag that's set the first time end-of-file is reached and can only be reset by calling clearerr or performing a successful fseek or rewind. Thus, once getc returns EOF once, it will keep returning EOF, even if new data becomes available, unless you use one of the aforementioned methods for clearing the eof flag.
Some non-conformant implementations may immediately make new data available. This behavior is harmful and can break conformant applications.
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