我的程序总是停止工作:S (C++)
我编写了一个程序来从文件中获取数据，它可以工作，但是程序说它停止工作。 这是我的代码：
#include <stdio.h>
#include <windows.h>
#include <iostream>
using namespace std;
string show()
{
FILE *in;
char c;
in = fopen("version.txt", "r");
if(in != NULL)
{
while((c = fgetc(in)) != EOF)
{
putchar(c);
}
fclose(in);
}
else printf("Unable to open file\n");
}
int main()
{
show();
}
I made a program to get data from a file, it works, but then the program says it stopped working.
Here is my code:
#include <stdio.h>
#include <windows.h>
#include <iostream>
using namespace std;
string show()
{
FILE *in;
char c;
in = fopen("version.txt", "r");
if(in != NULL)
{
while((c = fgetc(in)) != EOF)
{
putchar(c);
}
fclose(in);
}
else printf("Unable to open file\n");
}
int main()
{
show();
}
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评论（5）
您的函数被声明为返回一个
字符串，但没有 return 语句。这是 C++ 中的“未定义行为”（仅在
main中，您可以省略 return 语句，在这种情况下，C++ 将自动假定return 0;- 但 IMO最好也总是写它）。Your function is declared to return a
stringbut there is no return statement.This is "undefined behavior" in C++ (only in
mainyou are allowed to omit the return statement and in that case C++ will assume areturn 0;automatically - but IMO it's nicer to also always write it).fgetc man 说：
fgetc() 从流中读取下一个字符并将其作为unsigned char 转换为 int
当循环到达文件末尾时，
fgetc返回 EOF，它位于 int 上。当您将其转换为字符时，您的条件将始终返回 true。在测试其值是否为 EOF 之前，必须将 c 的类型更改为 int。fgetc man says:
fgetc() reads the next character from stream and returns it as anunsigned char cast to an int
When your loop reaches the end of the file,
fgetcreturns EOF, which is on a int. As you cast it to a char, your condition will always return true. You must change the type of c to an int before testing if its value is EOF.您必须返回一些字符串，例如 return "";
问候。
You must return some string, for example return "";
Regards.
只需将
string show()更改为void show()即可。那会解决你的问题。Just change
string show()tovoid show(). That will solve your problem.这里有很多错误或模糊的事情。
首先：决定必须是 C 还是 C++。在 C++ 中，还有其他读取文件的方法（请参阅 std::fstream）
第二：删除不需要的标头。包括 stdio 和 iostream（它们产生类似的东西，一个用于 C，另一个用于 C++，意味着不清楚您实际想要做什么！）
第三：包括 windows.h 意味着编译所有 Windows API 声明。那是你根本没用过！这样做的目的是什么？
第四：
show中string的作用是什么？ string 是 C++ 类型，在所有输入都用 C 编写的程序中。而且您没有返回任何内容！第五：
fgetc返回 int。您很可能遇到EOF 陷阱。Lots of wrong or fuzzy things here.
First: decide if this has to be C or C++. In C++ there are other methods to read files (see
std::fstream)Second: remove not needed headers. Including both stdio and iostream (that make similar things, one for C the other for C++, means having a non clear idea of what you're actually want to do!)
Third: including windows.h means compile all the windows API declarations. That you're not using at all! What was the purpose of that?
Fourth: What's the purpose to
stringinshow? string is a C++ type, in a program where all input had been written in C. And you didn't return anything!Fifth:
fgetcreturn as int. You're most likely running into the EOF pitflall.