c - 为什么我的输出为空？

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

int main(){

    char str [1000] = "";
    char ch     = 'M';
    char *findM;
        printf("Enter a line of text\n");
        scanf("%s", str);
            findM = strchr(str, ch);
        printf("string after %c is %s ", ch, findM);

    return 0;
}

程序的输入是“我的名字是Steve”，并且该程序的输出变为，M之后的字符串是(null)为什么会发生这种情况？

Answer 1

正如评论之一中提到的，scanf("%s", str) 读取直到找到尾随空格。在您输入的“My name is Steve”中，scanf 将读取到 My，因为 My 后面有一个空格。

Assuming that your input only contains numbers,letters, and spaces you could try the following:

int main() 
{
    char str[1000] = "";
    char ch = 'M';
    char *findM;
    printf("Enter a line of text\n");
    scanf("%999[0-9a-zA-Z ]", str); // Get all alphanumerics and spaces until \n is found
    findM = strchr(str, ch);
    findM++; // Increment the pointer to point to the next char after M
    printf("string after %c is %s ", ch, findM);

    return 0;
}

If you are not required to use scanf(), I will recommend staying away from scanf() and using fgets() instead:

int main()
{

    char str[1000] = "";
    char ch = 'M';
    char *findM;
    printf("Enter a line of text\n");
    fgets(str, sizeof(str), stdin); // Get the whole string
    findM = strchr(str, ch);
    findM++; // Increase the counter to move to the next char after M
    printf("string after %c is %s ", ch, findM);

    return 0;
}