读取/ proc / cpuinfo并在C中打印匹配行

Question

I am currently working on a C program to get specific CPU Information like the cpu model or how many cores the cpu has.

On Linux one way is to read "/proc/cpuinfo". Problem: I don't want everything to be printed out. Only the lines containing "model name" and "cpu cores" is what I want to be printed out.

1. Open file and print its content: done

#include <stdio.h>

int main() {
    char cpuinfo;
    FILE *fp = fopen("/proc/xcpuinfo", "r");

    if (fp == NULL) {
        fprintf(stderr, "Error opening file\n");
    } else {
        while ((cpuinfo = fgetc(fp)) != EOF) {
            printf("%c", cpuinfo);      
        }
        fclose(fp);
    }

    return 0;
}

2. Print only the lines containing "model name" & "cpu cores": not done

Answer 1

A simple solution with POSIX getline :

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <stdlib.h>

int main() {
        FILE *fp = fopen("/proc/cpuinfo", "r");
        assert(fp != NULL);
        size_t n = 0;
        char *line = NULL;
        while (getline(&line, &n, fp) > 0) {
                if (strstr(line, "model name") || strstr(line, "cpu cores")) {
                        printf("%s", line);
                }
        }
        free(line);
        fclose(fp);
        return errno;
}

Without getline you can use big enough line buffer char buf[200]; and use fgets(buf, sizeof(buf), fp) or you could implement a simple getline yourself.

Answer 2

Another option is to pass the filename and terms to search for as arguments to the program rather than hardcode the filename and search terms. With your search terms, you can compare against the same number of leading characters in each string with strncmp and output any matching lines (or store them, etc..)

While fgetc will read a single character at a time, fgets (like POSIX getline ) are line-oriented input functions and will read an entire line at a time (provide with a sufficiently sized buffer -- don't skimp on buffer size )

Putting things together so that the program accepts the filename to read as the first argument, and then any number of search terms (to the limits of argv ) as subsequent arguments, you could do something similar to:

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

#define MAXC 2048   /* if you need a constant, #define one (or more) */

int main (int argc, char **argv) {

    char buf[MAXC]; /* buffer to hold each line in file */ 
    FILE *fp = argc > 1 ? fopen (argv[1], "r") : NULL;  /* open file */

    if (!fp) {  /* validate file open for reading */
        perror ("file open failed");
        return 1;
    }

    while (fgets (buf, MAXC, fp)) {                 /* read each line */
        for (int i = 2; i < argc; i++) {            /* loop over terms */
            char *cmpstr = argv[i];                 /* compare string */
            size_t cmplen = strlen (cmpstr);        /* length to compare */
            if (strncmp (buf, cmpstr, cmplen) == 0) /* does start match? */
                fputs (buf, stdout);                /* output string */
        }
    }
    fclose (fp);                                    /* close file */

    return 0;
}

Example Use/Output

$ ./bin/cmpleadingstr2 /proc/cpuinfo "model name" "cpu cores"
model name      : Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu cores       : 2
model name      : Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu cores       : 2
model name      : Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu cores       : 2
model name      : Intel(R) Core(TM) i7-2620M CPU @ 2.70GHz
cpu cores       : 2

or

$ ./bin/cmpleadingstr2 /proc/cpuinfo "processor"
processor       : 0
processor       : 1
processor       : 2
processor       : 3