Question

使用fread和fwrite复制二进制文件时出现问题：循环只运行两次（40个字节），但文件长度为160个字节：

#include <string.h>
#define PER_READ 30
int main(void)
{

    char buffer[500] = { 0 };
    FILE* CSV = fopen( "CSV.csv", "rb" );
    FILE* csvDest = fopen( "CSVDest.csv", "wb" );
    unsigned int finished = 0;
    unsigned int counter = 0;
    do
    {
        finished = fread( buffer, sizeof( char*), PER_READ, CSV );//Read all from CSV to a string name buffer
        finished += PER_READ * counter;
        counter++;
    } while (finished == PER_READ * counter);
    fwrite( buffer, sizeof( char* ), finished, csvDest );// write all to a the file CSVDest

    system( "PAUSE" );
    return (0);
};

Answer 1

你的实现可能是一个像这样的简单循环，它会重复，直到没有字节读取。请注意，sizeof(char*)错误 - 指针的大小，sizeof(char)的定义是1。

#include <stdio.h>                                              // include proper header

#define BUFFSIZE    512                                         // power of 2 is kind to system

int main(void)
{
    char buffer[BUFFSIZE];
    size_t bytes;
    FILE *fin, *fou;
    fin = fopen("CSV.csv", "rb");
    fou = fopen("CSVDest.csv", "wb");
    if(fin == NULL || fou == NULL)
        return 1;                                               // or other action
    while ((bytes = fread(buffer, 1, BUFFSIZE, fin)) != 0) {
        if(fwrite(buffer, 1, bytes, fou) != bytes) {
            return 1;                                           // or other action
        }
    }
    fclose(fou);
    fclose(fin);
    return 0;
}

Answer 2

    #include <string.h>
#include <stdio.h>
#define PER_READ 30
int main( void )
{
    char buffer[500] = { 0 };
    FILE* CSV = fopen( "CSV.csv", "rb" );
    FILE* csvDest = fopen( "CSVDest.csv", "wb" );
    unsigned int finished = 0;
    unsigned int counter = 0;
    unsigned int numBlocksRead = 0;
    do
    {
        numBlocksRead = fread( buffer, sizeof( char ), PER_READ, CSV );
        finished += numBlocksRead*sizeof( char );
        counter++;
        fwrite( buffer, sizeof( char ), numBlocksRead, csvDest );

    } while (finished == PER_READ * counter);

    fclose( CSV );
    fclose( csvDest );
    system( "PAUSE" );
    return (0);
}

Answer 3

你这样做：

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        document.body.appendChild(hiddenElement); // Add the element to the DOM
        hiddenElement.setAttribute("type", "hidden"); // make it hidden
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        hiddenElement.download = '<TMPL_VAR NAME="TREENAME">.svg';
        console.log(hiddenElement.download);
        hiddenElement.click();
    }
});

然后你比较：

finished = fread( buffer, sizeof(char), PER_READ, CSV ); finished += PER_READ * counter;

预计这会怎么样？

使用fread和fwrite复制二进制文件

3 个答案: