[英]Strangeness in reading a binary file in C
I've defined a binary file like this in C 我已经在C中定义了这样的二进制文件
FILE *gfp;
gfp = fopen(gridfiles, "wb");
The variable gridfiles stores the name of the file, and has been defined earlier. 变量gridfiles存储文件的名称,并且已在前面定义。 Now I write out two variables into the file. 现在,我将两个变量写到文件中。
for(yy = 0; yy < nfiley; yy++) {
for(xx = 0; xx < nfilex; xx++) {
filebx = beguv + xx*1E3;
fileby = enduv - yy*1E3;
fwrite(&filebx, sizeof(filebx), 1, gfp);
fwrite(&fileby, sizeof(fileby), 1, gfp);
}
}
If right after this code I 如果在此代码之后我
fseek(gfp, 0, SEEK_SET);
fread(&filebx, sizeof(filebx), 1, gfp);
fread(&fileby, sizeof(fileby), 1, gfp);
fprintf(stderr, "%f %f", filebx, fileby);
my output is 我的输出是
1000 15000
for the first two, which is as expected. 对于前两个,这是预期的。
But if after some assorted other code (that doesn't involve these files at all) I repeat the fseek() etc., my output is 但是,如果在一些其他代码(根本不涉及这些文件)之后,我重复fseek()等,我的输出是
14000 14000
regardless of what I do. 不管我做什么 I've been trying to figure this out for a while now... anyone know what I'm doing wrong? 我已经尝试了一段时间了……有人知道我在做什么错吗?
It's Undefined Behaviour to read from a stream which has been opened in write mode. 从以写模式打开的流中进行读取是未定义的行为 。 You should make it: 您应该做到:
gfp = fopen(gridfiles, "wb+");
if you plan to both read and write. 如果您打算同时读写。
Also, as pointed out by @Kyle Jones in the comments above, you should get into the habit of checking the return status of fread
/ fwrite
when doing file I/O - this would have caught your problem a lot earlier. 另外,正如@Kyle Jones在上述评论中指出的那样,您应该养成在执行文件I / O时检查fread
/ fwrite
返回状态的习惯-这会早点解决您的问题。
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