[C++知识库]文件操作/16进制/10进制/8进制

将16进制（2个字符表达的）转成十进制整数

#include <stdio.h>
/*
将16进制（2个字符表达的）转成十进制整数
*/
//需要用到将大写字母转化为小写字母
int tolower(int c)
{   
    if(c >= 'A' && c <= 'Z')
    {
        c = c + 'a' - 'A';
    }
    return c;
}

int htoi(char *s)
{   
    int i;
    int n = 0;
    //首先查看是否是0x形式
    if(s[0] == '0' && (s[1] == 'x' ||s[1] == 'X'))
    {
        i = 2;
    }
    else
    {
        i = 0;
    }
    for(;(s[i] >= '0' && s[i] <= '9')||(s[i] >= 'a'&& s[i] <= 'z')||(s[i] >= 'A' && s[i] <= 'Z');i++)
    {
        if(tolower(s[i]) >= 'a' && tolower(s[i]) <= 'z')
        {
            n = 16 * n + 10 + (tolower(s[i]) - 'a');
        }
        else
        {
            n = 16 * n + (tolower(s[i]) - '0');
        }
    }
    return n;
}
int main()
{
    char* s1 = "0x11";
    char* s2 = "11";
    int n1 = htoi(s1);
    int n2 = htoi(s2);
    printf("n1 = %d, n2 = %d\n",n1,n2);
    return 0;
}#include <stdio.h>
/*
将16进制（2个字符表达的）转成十进制整数
*/
//需要用到将大写字母转化为小写字母
int tolower(int c)
{   
    if(c >= 'A' && c <= 'Z')
    {
        c = c + 'a' - 'A';
    }
    return c;
}

int htoi(char *s)
{   
    int i;
    int n = 0;
    //首先查看是否是0x形式
    if(s[0] == '0' && (s[1] == 'x' ||s[1] == 'X'))
    {
        i = 2;
    }
    else
    {
        i = 0;
    }
    for(;(s[i] >= '0' && s[i] <= '9')||(s[i] >= 'a'&& s[i] <= 'z')||(s[i] >= 'A' && s[i] <= 'Z');i++)
    {
        if(tolower(s[i]) >= 'a' && tolower(s[i]) <= 'z')
        {
            n = 16 * n + 10 + (tolower(s[i]) - 'a');
        }
        else
        {
            n = 16 * n + (tolower(s[i]) - '0');
        }
    }
    return n;
}
int main()
{
    char* s1 = "0x11";
    char* s2 = "11";
    int n1 = htoi(s1);
    int n2 = htoi(s2);
    printf("n1 = %d, n2 = %d\n",n1,n2);
    return 0;
}

写入文件格式

• 以16进制写入文件

• C 库函数 int fprintf(FILE *stream, const char *format, …) 发送格式化输出到流 stream 中。

• 头文件<stdio.h>

int fprintf(FILE *stream, const char *format, ...)
如：
fprintf(f,"%02x",ch1);

c语言中文网整理得不错

 char* s1 = "0x11";
 gdb调试：
 (gdb) p *s1@7
$4 = "0x11\000\061\061"
(gdb) p/x *s1@7
$6 = {0x30, 0x78, 0x31, 0x31, 0x0, 0x31, 0x31}
(gdb) p *s1@7
$7 = "0x11\000\061\061"
(gdb) p *s1@5
$8 = "0x11"

43          char* s1 = "0x112";
(gdb) p *s1
$1 = 48 '0'
(gdb) p *s1[1]
Cannot access memory at address 0x78
(gdb) p s1[1]
$2 = 120 'x'
(gdb) p *s1@8
$3 = "0x112\000\061\061"
(gdb) p/x *s1@8
$4 = {0x30, 0x78, 0x31, 0x31, 0x32, 0x0, 0x31, 0x31}

一直没懂

\061

是啥？
解释：
八进制ASCII码值61，即十进制49，意思是字符’1’。

(gdb) p/o *s1@8
$5 = {060, 0170, 061, 061, 062, 0, 061, 061}