C语言 如何从文件中逐字节读取
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原文地址: http://stackoverflow.com/questions/17362046/
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how to read byte by byte from a file
提问by Zisis Diamantis
I want to read the 4 first bytes from a binnary file which is a song.wav type. In a .wav file the 4 first bytes must be 52-46-49-49 and I have to read them to check later if they are true.
我想从一个 Song.wav 类型的二进制文件中读取前 4 个字节。在 .wav 文件中，前 4 个字节必须是 52-46-49-49，我必须阅读它们以便稍后检查它们是否正确。
The thing is that I have a compile arror at the fread line which says invalid conversion from "unsigned char" to "void"and initialzing argument 1 of 'size_t fread(void*,size_t,size_t,FILE*)and i dont know what it means.
事情是，我在FREAD线，说：编译arrorinvalid conversion from "unsigned char" to "void"和 initialzing argument 1 of 'size_t fread(void*,size_t,size_t,FILE*)，我不知道这意味着什么。
I saw in a previous topic tha this is the way that fread must be done if i want to read byte by byte. If anyone has any idea of how i can read byte by byte and store them in an array that be great. Thank you.
我在上一个主题中看到，如果我想逐字节读取，这是必须完成 fread 的方式。如果有人知道我如何逐字节读取并将它们存储在一个很棒的数组中。谢谢你。
void checksong(char *argv[]){
FILE *myfile;
int i;
unsigned char k[4];
myfile=fopen(argv[2],"r");
i=0;
for(i=0; i<4; i++){
fread(k[i],1,1,myfile);
}
for(i=0; i<4; i++){
printf("%c\n", k[i]);
}
return ;
}
回答by Elazar
It is a single error:
这是一个单一的错误：
Invalid conversion from
unsigned chartovoid*initializing argument 1 ofsize_t fread(void*,size_t,size_t,FILE*)
从
unsigned char到void*初始化参数 1 的无效转换size_t fread(void*,size_t,size_t,FILE*)
It means k[i]is an unsigned char, and not a pointer. You should use &k[i]or k+i.
这意味着k[i]是一个unsigned char，而不是一个指针。您应该使用&k[i]或k+i。
However, you don't really need to read byte by byte. You can read 4 bytes, no loops involved:
但是，您实际上并不需要逐字节读取。您可以读取 4 个字节，不涉及循环：
fread(k, 4, 1, myfile);
Printing the numbers:
打印数字：
for (i=0; i<4; i++)
printf("%d\n", k[i]);
回答by rectummelancolique
In order to read exactly one byte and store it into kat index i, you need to provide the address of element i
为了准确读取一个字节并将其存储到k索引处i，您需要提供元素 i 的地址
for(i=0; i<4; i++){
fread(&k[i],1,1,myfile);
}
However, you'd rather read the whole 4 bytes in one go if you're interested in them 4. So no forloop at all, and just do:
但是，如果您对它们 4 感兴趣，您宁愿一次读取整个 4 个字节。所以根本没有for循环，只需执行以下操作：
fread(k,1,4,myfile);
It is also good practice to test the return code of fread(and any I/O operation for that matter) in case it fails. man freadfor more information.
测试返回代码fread（以及与此相关的任何 I/O 操作）以防万一失败也是一种很好的做法。man fread想要查询更多的信息。
回答by rectummelancolique
You can use just
你可以只使用
char buffer[4];
fread(buffer,1,4,myfile);
回答by Laksith
you need not to use fread()Even the fgetc()works well. Simple coding. SImple as reading a text file.
你不需要使用fread()Evenfgetc()效果很好。简单的编码。就像读取文本文件一样简单。
#include <stdio.h>
int main(int argc, char** argv)
{
FILE* f = fopen("lak", "rb");
fseek(f,0,SEEK_END);
long lsize=0,i=0;
lsize = ftell(f);
rewind(f);
while(i<lsize){
int first = fgetc(f);
i++;
printf("first byte = %x\n", (unsigned)first); //you can do anything with
//first now
}
fclose(f);
return 0;
}
