C语言 在 C 中使用 fopen_s
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Using fopen_s in C
提问by nikodamn
I have a problem with programming in C, especially with fopen in Visual Studio. I read about the fopen_sfunction and added the following line to my project, but it still doesn't work.
我在用 C 编程时遇到问题，尤其是在 Visual Studio 中使用 fopen。我阅读了该fopen_s函数并将以下行添加到我的项目中，但它仍然不起作用。
_CRT_SECURE_NO_WARNINGS
So I tried using fopen_sin this way:
所以我尝试fopen_s以这种方式使用：
FILE *fp;
errno_t err;
if ((err = fopen_s(&fp, "C:/File.txt", "rt")) != 0)
printf("File was not opened\n");
else
fprintf(fp, "Date: %s, Time: %s, Score: %i \n", __DATE__, __TIME__, score);
fclose(fp);
It's still crashing. What's wrong?
它仍然崩溃。怎么了？
采纳答案by hyde
You use fclosewith an invalid fpvalue, even if opening failed. Add {}around the elsebranch, at least.
即使打开失败，您也使用fclose无效fp值。至少{}在else分支周围添加。
Many developers think it is generally a good idea to use braces everywhere, even with one statement inside them. It's so easy to make a mistake like this if you don't, even for experienced developers. So put them around the thenbranch too.
许多开发人员认为在任何地方都使用大括号通常是个好主意，即使其中包含一个语句。如果不这样做，很容易犯这样的错误，即使对于有经验的开发人员也是如此。所以也把它们放在then分支周围。
回答by zwol
The _sfunctions are unportable Microsoft inventions which, for the most part, duplicate functionality that already existed under a more portable name. Moreover, blindly changing from the non-_svariant of a function to the _svariant generally does notfix anything. (For instance, silently truncating a string is less disastrousthan clobbering the stack but it is still misbehavior which may be exploitable.)
这些_s功能是不可移植的 Microsoft 发明，在大多数情况下，它们复制了已经存在于更可移植名称下的功能。此外，盲目从非改变_s功能的变体的_s变异一般不会不解决任何事情。（例如，默默地截断一个字符串比破坏堆栈更不具有灾难性，但它仍然是可能被利用的不当行为。）
Your problem -- which is not affected by the difference between fopenand fopen_s-- is almost certainly that you are not bothering to check for errors properly. Here is how to check for errors properly:
您的问题——不受fopen和之间差异的影响fopen_s——几乎可以肯定是您没有费心去正确检查错误。以下是正确检查错误的方法：
#include <stdio.h>
#include <string.h>
#include <errno.h>
int main(int argc, char **argv)
{
FILE *fp;
if (argc != 2) {
fprintf(stderr, "usage: %s filename\n", argv[0]);
return 2;
}
fp = fopen(argv[1], "rb");
if (!fp) {
fprintf(stderr, "opening %s: %s\n", argv[1], strerror(errno)); // HERE
return 1;
}
// use 'fp' here...
return 0;
}
Notice how the line marked // HEREprints boththe exact string that was passed to fopenand the result of strerror(errno). It is absolutely essential that you print both the arguments and strerror(errno)whenever a system call fails. (Note: If you do wind up using one of the _sfunctions that returns an error code rather than setting errno, then you must pass the return value to strerrorinstead.)
注意，此时的行标// HERE印双方传递给确切的字符串fopen和结果strerror(errno)。打印参数和strerror(errno)系统调用失败时都非常重要。（注意：如果您确实使用_s了返回错误代码而不是设置的函数之一errno，那么您必须将返回值传递给strerror。）
Change your program to do this and you will be able to figure out whyit isn't working.
更改您的程序以执行此操作，您将能够弄清楚它为什么不起作用。
回答by Achamyeleh Dagnaw
//give it a shot, it's working.
//试一试，它正在工作。
#include <stdio.h>
#include <tchar.h>
#include<iostream>
using namespace std;
int main()
{
int score = 10;
FILE *fp;
errno_t err;
if ((err = fopen_s(&fp, "C:\Users\achea\Desktop\File.txt", "w+")) != 0)
{
printf("File was not opened\n");
}
else
{
fprintf(fp, "Date: %s, Time: %s, Score: %i \n", __DATE__, __TIME__,
score);
}
fclose(fp);
return 0;
}
回答by binit92
On Windows the slashes are different than on Linux, so you may consider using C:\File.txt instead of C:/File.txt.
Windows 上的斜杠与 Linux 上的不同，因此您可以考虑使用 C:\File.txt 而不是 C:/File.txt。
回答by vmp
Regarding the mode you are using to open,
关于您使用的打开模式，
err = fopen_s(&fp, "C:/File.txt", "rt")
I never used the letter t as a parameter and don't know what that is for...
我从来没有用过字母 t 作为参数，也不知道它是干什么用的……
But you are opening with R (read) and trying to write...
但是您正在使用 R（读取）打开并尝试编写...
Try
尝试
err = fopen_s(&fp, "C:/File.txt", "w")
or
或者
err = fopen_s(&fp, "C:/File.txt", "w+")
Also, you don't really need the err variable. If the fopen call fails, the pointer will be NULL.
此外，您实际上并不需要 err 变量。如果 fopen 调用失败，则指针将为 NULL。
