用％s打印字符串会打印错误的数据 [英] Printing string with %s prints wrong data

问题描述

我正在使用fread函数从文件读取字符串，然后打印字符串。
我将字符串定义为具有LONGNUM大小（预定义值）的字符数组。
我每次读取1个元素，每个字节1个字节。
在使用以下命令打印字符串时：printf（读取的字符串为：％s\n，buffer）;
的输出是：读取的字符串是b
我不明白，为什么在字符串结尾最后得到这个值？
当使用以下命令打印字符串时：printf（读取的字符串为：％c\n，buffer [0]）;
我得到没有值的写输出。
请向我解释原因。

I'm reading from file to string with fread function and then printing the string. I defined the string as array of chars with LONGNUM size(pre defined value). I'm reading 1 element 1 byte size each time. when printing the string with : printf("the string that read is: %s\n",buffer); the output is : the string that read is b I don't get it, why in the end of the stringi get this values? when printing the string with : printf("the string that read is : %c\n",buffer[0]); I get the write output without values. please explain me why.

代码为

#include <stdio.h>
#define LONGNUM 1

void main(int argc,char *argv[])
{

    FILE * src;
    FILE * dst;
    int num;
    char buffer[LONGNUM];

    // argc is the number of the elements in argv
    // the first argv element is the name of the program

    if(argc < 3){
        printf("prototype error <source path> <dest path>\n");
        return;
    }
    printf ("source  path is : %s \n",argv[1]);
    printf ("dest path is : %s \n",argv[2]);

    src = fopen(argv[1],"r");

    while(!(feof(src))){
        num = fread(buffer,1,1,src);
        printf("the number of items read %d\n",num);
        printf("the string that read is %s\n",buffer);
        //printf("the string that read is %c\n",buffer[0]);

    }

}

我想要您告诉我什么是写方法。
谢谢。

I would like you to advise me what is the write way to do it. Thanks.

推荐答案

％s说明符期望空终止字符串。 fread不会以null终止字符串，因此您看不到正确的输出。由于缓冲区的长度为1，因此％c是要打印的正确说明符。

%s specifier expects null termination string. fread does not terminate string with null, so you don't see correct output. since buffer is of length 1, %c is the correct specifier to print.

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