Detailed explanation of the example of returning values ​​of other processes in C language popen function calling

Preface

When we want to call an existing program in C language and want to get the program return value instead of outputting it in the terminal, we must call itpopen( )The function is here.

popen( ) A pipeline is created and a new process is started, through which inter-process communication is conducted.popen( )Returns a file pointer, similarfopen( ), but the file pointer is not used to read or write to the input/output of the child process.

popen( )There are two modes for functions: read moderand write modew. In read mode, data is read from the output of the child process; in write mode, data is written to the input of the child process.

1. popen( ) function prototype

popen( )In the standard library<>Function prototype in:man documentation

#include <>
       FILE *popen(const char *command, const char *type);
       int pclose(FILE *stream);

File pointers need to be recycled,pclose( )Function.

2. Usage examples (provided by AI)

The following code can be used in both Linux and Windows,ls -lIt is a Linux command used to display the contents of the specified working directory (list the files and subdirectories contained in the current working directory).

#include <>
int main()
{
    FILE *fp;
    char buffer[1024];
    // Execute the command and read the output    fp = popen("ls -l", "r");
    if (fp == NULL)
    {
        printf("Cannot execute command\n");
        return 1;
    }
    // Read the output and print it    while (fgets(buffer, sizeof(buffer), fp) != NULL)
    {
        printf("%s", buffer);
    }
    // Close the file pointer    pclose(fp);
    return 0;
}

Summarize

I used it in an articlepopen( )Function Callwmic cpu getCommands, and output them into the program to interpret the computer's cpu properties.

Although the C language textbook will not introduce this standard library function, since it is so useful, I will master it.

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