[英]C - Using fscanf for reading hexadecimal and characters from files
I have two files.我有两个文件。 The first file (in the pointer
key_file
) has the following content in hexadecimal (notice that every two characters corresponds to a hexadecimal byte):第一个文件(在指针
key_file
)具有以下十六进制内容(注意每两个字符对应一个十六进制字节):
18FC5E66F9F205488BFC0E9E
And the other file (in the pointer p_text_file
) has the following content另一个文件(在指针
p_text_file
)具有以下内容
hernandariov
I want to write the bitwise XOR between these two values and save the result in another file (in the pointer c_text_file
).我想在这两个值之间写入按位异或并将结果保存在另一个文件中(在指针
c_text_file
)。 I write the following (abbreviated) code in C:我在 C 中编写了以下(缩写)代码:
char p_text_char;
unsigned char k_char;
for(int i = 0; i < LEN; i++) {
fscanf(key_file, "%2hhX", &k_char);
fscanf(p_text_file, "%c", &p_text_char);
fprintf(c_text_file, "%02X", k_char ^ p_text_char);
}
But when I execute the code, it exits with a non-zero value, ie, there is an error.但是当我执行代码时,它以非零值退出,即出现错误。 After try many solutions, I found that if I change the type of
p_text_char
to int
, the code works pretty well, but I want to know why.在尝试了很多解决方案后,我发现如果将
p_text_char
的类型p_text_char
为int
,代码运行得很好,但我想知道为什么。 In fact, I want to keep p_text_char
as char
and k_char
as unsigned char
because these are the natural types and sizes for this variables in the problem I am working on (the one-time-pad encryption scheme).事实上,我想将
p_text_char
保留为char
并将k_char
为unsigned char
因为这些是我正在处理的问题(一次性加密方案)中此变量的自然类型和大小。 I am working on Windows with MinGw compiler.我正在使用 MinGw 编译器在 Windows 上工作。
Thank you.谢谢你。
- EDIT - - 编辑 -
After run a debugger in this code, I found that there is a "segmentation fault".在这段代码中运行调试器后,我发现存在“分段错误”。 I try to minimize the code in order to find the error.
我尝试最小化代码以找到错误。 First, I try the following code with the files as showed before:
首先,我对之前显示的文件尝试以下代码:
#include <stdio.h>
#define LEN 12
int main() {
FILE *key_file;
key_file = fopen("key.txt", "r");
if(key_file == NULL) {
printf("ERROR: cannot read the files.");
return 1;
}
unsigned char k_char;
for(int i = 0; i < LEN; i++) {
fscanf(key_file, "%2hhX", &k_char);
}
fclose(key_file);
return 0;
}
After one iteration of the for loop, the VS Code editor shows me a "segmentation fault".在 for 循环的一次迭代之后,VS Code 编辑器向我显示了“分段错误”。 And when I change
k_char
to int
, everything works fine.当我将
k_char
更改为int
,一切正常。 I will keep posting my findings about this problem.我将继续发布我对这个问题的发现。
The version of VS C that OP is using may not understand "%hhX"
. OP 使用的 VS C 版本可能无法理解
"%hhX"
。 Formally this is undefined behavior and *scanf()
may ignore "hh"
.正式这是未定义的行为,
*scanf()
可能会忽略"hh"
。 Thus code "works" with an int
.因此代码与
int
一起“工作”。
To cope with C89-like compilers that lack "hh"
understanding, use an intermediate object.要处理缺乏
"hh"
理解的类 C89 编译器,请使用中间对象。
// fscanf(key_file, "%2hhX", &k_char);
unsigned utemp = 0;
fscanf(key_file, "%2X", &utemp);
k_char = utemp;
... or use a compiler that conforms at least to the 21 year old C99 standard, if not C11 or C17. ...或者使用至少符合 21 年历史的 C99 标准的编译器,如果不是 C11 或 C17。 C2x due out in a year or two.
C2x 在一两年内到期。
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