c - C语言中的fputc在遇到字符 "d5dc"时将错误的数据写入文件

Question

i want to convert text file to binary.

for example:

"0100ed73 ed000032 0100d5dc d5dc0012"

every eight char need be converted to a int. part of my program is:

for(int i=0;i<4;i++)
{
    start = tmp+i*9;
    for(int j=0;j<4;j++)
    {
        unsigned char a = ctoi(start[0+j*2])*16+ctoi(start[1+j*2]);
        fputc(a,outFilePtr);            
    }

}
unsigned int ctoi(char in)
{
    if(in>='0'&&in<='9')
    {
        return in -'0';
    }
    else
    {
        return in - 'a' + 10;
    }
}

at most time it is right.but after the program convert the char "d5dc",the out file no more match the in file.

提前感谢您的帮助。

Answer 1

围绕问题中显示的代码提供最小的代码集，并添加诊断打印，会生成 MCVE( Minimal, Complete, Verifiable Example ，如下所示:

#include <stdio.h>

static unsigned int ctoi(char in);

int main(void)
{
    char tmp[] = "0100ed73 ed000032 0100d5dc d5dc0012";
    FILE *outFilePtr = stdout;
    fprintf(stderr, "Hex data: [%s]\n", tmp);

    for (int i = 0; i < 4; i++)
    {
        char *start = tmp + i * 9;
        for (int j = 0; j < 4; j++)
        {
            unsigned char a = ctoi(start[0 + j * 2]) * 16 + ctoi(start[1 + j * 2]);
            fputc(a, outFilePtr);
            fprintf(stderr, "0x%c%c = 0x%.2X = '%c'\n", start[0 + j * 2], start[1 + j * 2], a, a);
        }
    }
    putchar('\n');
    return 0;
}

static unsigned int ctoi(char in)
{
    if (in >= '0' && in <= '9')
    {
        return in - '0';
    }
    else
    {
        return in - 'a' + 10;
    }
}

并且，当通过将非打印字符转换为 \xXX 十六进制转义序列的程序运行输出时，输出为:

Hex data: [0100ed73 ed000032 0100d5dc d5dc0012]
0x01 = 0x01 = '\x01'
0x00 = 0x00 = '\x00'
0xed = 0xED = '\xED'
0x73 = 0x73 = 's'
0xed = 0xED = '\xED'
0x00 = 0x00 = '\x00'
0x00 = 0x00 = '\x00'
0x32 = 0x32 = '2'
0x01 = 0x01 = '\x01'
0x00 = 0x00 = '\x00'
0xd5 = 0xD5 = '\xD5'
0xdc = 0xDC = '\xDC'
0xd5 = 0xD5 = '\xD5'
0xdc = 0xDC = '\xDC'
0x00 = 0x00 = '\x00'
0x12 = 0x12 = '\x12'
\x01\x00\xEDs\xED\x00\x002\x01\x00\xD5\xDC\xD5\xDC\x00\x12

从表面上看，您的代码准确地生成了它应该生成的输出，因此不清楚您在哪里出现问题 - 除非它可能不直接出现在问题中显示的代码中。