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# Example: putenv

The following example uses putenv to create a new environment variable LOGFILE_NAME. It is retrieved later on with the getenv function and used to write to the log file in the system's temporary directory.

        #include <stdio.h>

        char * tmp, logfile[512], dir_separator;
        FILE* file;

        // Create an environment variable

        putenv("LOGFILE_NAME=lr_test.txt");

        // Retrieve the temporary directory environment directory

        if(tmp = (char *)getenv("TEMP"))
            lr_output_message ("Temp Dir = %s", tmp);
        else {
            lr_output_message ("TEMP environment variable undefined");
            return -1;
        }

        sprintf(logfile, "%s\\%s", tmp, (char *)getenv("LOGFILE_NAME"));

        // Open and write to the log file

        if ((file = fopen(logfile, "w")) == NULL ) {
            lr_error_message ("Cannot open %s", logfile);
            return -1;
        }
        else
            lr_output_message ("Opened %s", logfile);

        fprintf(file, "this is a log file\n");
        fclose(file);

    Example: Output:
    Action.c(11): Temp Dir = D:\TEMP
    Action.c(24): Opened D:\TEMP\lr_test.txt

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