如何使用函数 sscanf 读取特定字符? [英] How can I use the function sscanf to read specific characters?

问题描述

我想从文件中读取信息，并将文件中a 的值赋给a"，将b 的值赋给b".但是没有用.

#include #include #include int main() {文件 *fp;字符缓冲区[1024]；查拉[128];字符 zahlb[128];字符子木[128];fp = fopen("./0312.conf", "r");如果(fp == NULL){perror("错误");返回 (-1);}而 (fgets(buffer, 1024, fp) != NULL) {sscanf(buffer, "%^", zimu);printf("zimu 是:%s\n", zimu);如果 (strcmp(zimu, "a") == 0) {sscanf(buffer, "%[1-9]s", zahla);}如果(strcmp(zimu，b")== 0){sscanf(buffer, "%[1-9]s", zahlb);}}printf("a=%s, b=%s\n", zahla, zahlb);}

文件内容为:

a=10b=5

解决方案

• 格式说明符 "%^" 没有意义，实际上不会做任何事情——所以你永远不会在 zimu 数组中得到任何东西.>

• 格式说明符中 %[1-9] 之后的 s 表示匹配文字 's' 字符"，因此永远不会匹配.您可能只想删除它.

• 由于您的输入行以 a= 或 b= 开头，"%[1-9]" 格式说明符将不匹配.

很可能你想要的是这样的

字符名称[100]，值[100]；if (sscanf(buffer, " %99[a-z] = %99[0-9]", name, value) == 2) {//匹配一个名称=值的行，用它做一些事情} 别的 {//不匹配——给出错误?}

• 在格式中使用空格字符来跳过空格——只要有空格，它就会跳过 0 个或多个空格字符.请注意 0 - 不需要空格，可以有任意数量的空格
• 始终检查返回值以查看预期的项目数是否匹配
• 您需要某种格式来匹配该行上的所有字符，但除了 %[ 和 %c 之外的格式说明符也将跳过空格，您可以如果您不关心尾随的东西，请忽略它.如果您确实关心尾随的内容，您可以使用 %n 来检查您扫描了多少个字符以确保它是整行.
• 在读取固定数组的 %s 和 %[ 说明符上使用边界以确保它们不会溢出.

I want to read the information from the file and give the value of a in file to the "a" and value of b to the "b". But it didn't work.

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

int main() {
    FILE *fp;
    char buffer[1024];
    char zahla[128];
    char zahlb[128];
    char zimu[128];

    fp = fopen("./0312.conf", "r");
    if (fp == NULL) {
        perror("error");
        return (-1);
    }
    while (fgets(buffer, 1024, fp) != NULL) {
        sscanf(buffer, "%^", zimu);
        printf("zimu is: %s\n", zimu);

        if (strcmp(zimu, "a") == 0) {
            sscanf(buffer, "%[1-9]s", zahla);
        }
        if (strcmp(zimu, "b") == 0) {
            sscanf(buffer, "%[1-9]s", zahlb);
        }
    }
    printf("a=%s, b=%s\n", zahla, zahlb);
}

the content of the file is:

       a=10
                b=5

解决方案

• The format specifier "%^" is meaningless and won't actually do anything -- so you never get anything in your zimu array.

• The s after %[1-9] in a format specifier means "match a literal 's' character", so will never match. You probably just want to remove it.

• Since your input lines start with a= or b=, the "%[1-9]" format specifiers will not match.

Most likely what you want is something like

char name[100], value[100];
if (sscanf(buffer, " %99[a-z] = %99[0-9]", name, value) == 2) {
    // matched a line with name=value, do something with it
} else {
    // didn't match -- give an error?
}

• use space characters in the format to skip whitespace -- whenever there is a space it will skip over 0 or more whitespace characters. Note the 0 -- a space is not required, and any number of spaces may be there
• ALWAYS check the return value to see if the expected number of items matched
• You need something in the format to match all the characters on the line, though format specifiers other than %[ and %c will also skip whitespace, and you can ignore trailing stuff if you don't care about it. If you do care about trailing stuff, you can use %n to check how many characters you scanned to make sure it is the entire line.
• use bounds on %s and %[ specifiers reading into fixed arrays to ensure that they don't overflow.

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